There are people out there that try to return anything no matter how stupid it is. And it's all so they can get some money. Here are the most insane reasons customers have given employees when returning an item.
“She Was Wearing It Backwards…”

“‘Not as described.’ It was a necklace featuring a word in a script font hanging on a chain. The customer’s complaint was that in the photos you could see the word when the model was wearing it, but when she tried hers on she could only see the word when looking in the mirror. Yeah, she was wearing it backwards.” (Source)
The Dead Bouquet.

“Guy tried to return flowers a week later because ‘they had died.’ Our flowers do not have any kind of ‘will last 5 days’ guarantee or anything. Called my manager and the customer argued with him for over half an hour about his £2 bouquet of flowers. My manager just sat there completely deadpan and every time the guy stopped talking said simply ‘I’m not refunding you for dead flowers’. When the guy eventually left (throwing his flowers on the floor) my boss cracked up and couldn’t stop laughing for several minutes.” (Source)
The Stale Cake.

“The other day, someone returned a birthday cake because it was stale. Was still in date and unopened. Somehow they knew it was stale without touching or tasting it.” (Source)
The Used Toilet.

“One time we had a guy try to return a camp toilet/potty thing claiming it had collapsed after it had been used. They’re not really stable things, essentially a heavy duty garbage bag splayed over an aluminum frame. He brought it back for us in a bigger garbage bag for us to check out, still full judging from the smell. We didn’t know what to do. No one was going to be checking inside that bag. So the manager at the time refunded him just to get him out of there, on the condition he disposed of the bag himself. He kept trying to put the bag up on the counter and open it up so we could see. So gross!” (Source)
The Not-So-Frozen Pizza.

“When I worked at Target in high school I was doing the customer service desk and this woman came in and returned 5 of the DiGiorno frozen pizza. They were all thawed and in soggy boxes and told me the reason is that they didn’t cook all the way through…Now I’ve eaten a lot of frozen pizza in my day and I’ve never seen one that didn’t cook all the way through, you may need to adjust times a bit but I think as an adult she should have been able to figure that out. Also, who buys that many of the same frozen pizza without knowing if they like it/having it before? But its target so we return whatever, I mark it for disposal, make a comment to the other person working the desk about what just happened, laughed for a second, and then moved on to the next person. Apparently that next person went and tracked down frozen pizza lady, told her what I said, and then she took offense to it and called to b—h at my boss about what I said and I got in trouble it sucked. So remember kids, people who can’t figure out how to cook a frozen pizza are the same people who get offended if you call them not smart enough to cook a frozen pizza.” (Source)
The Three-Year Return.

“A woman tried to return a three year old working grass cutter because her fingers had become too weak to pry open the case where the nylon cutter goes. We had tried for 20 minutes to make the case easier to open, but she wasn’t satisfied. She also had no receipt, and expected us to locate it on our network through her membership. When we told her she couldn’t possibly get a refund, she got mad and called us useless.” (Source)
Too hot.

“I had a woman want to return a pizza because it was delivered to her too hot.” (Source)
Not Hot Enough.

“I used to work at a McDonald’s. One time, someone ordered a tea with an absolutely stupid amount of milk. I don’t remember exactly how much, but the cup was basically half-filled with milk before I poured the hot water in. She sat down, sipped it once, and then demanded a refund because her tea was lukewarm. Another time, a woman ordered a meal with fries. When we gave her the meal, she said, ‘I’ll be right back’ and then went off to the washroom. About ten minutes later she comes back, picks up her meal, and then complains that her fries are cold. Thermal equilibrium, motherf**kers.” (Source)
The eBay sScammers.

“I’ve had a couple of people try to scam me by returning ebay items I sold them. Before I sell something I always take photos of the model number(s) and small unique marks that tell me that item is 100% my item. I sold somebody my old Nintendo Wii which worked perfectly fine and they claimed it was broken and wouldn’t run any discs. I told them they could send it back to me and I’d test it and give a refund if this were the case. I also mentioned I had photos of the exact Wii I sold them so I’d know if they were swapping it with a broken one to get their money back. They never replied or sent the Wii back.” (Source)
Mr. Magnum.

“We had a regular come in and whenever there was a woman in customer service, he’d try to return an opened box of condoms with the excuse ‘they were too small and he needed to exchange them for the Magnums’ instead. We let him do it once but then once it became an obvious habit and pick-up line, no more.” (Source)
False Advertisement.

“A guy ate a taco twelve pack then wanted me to refund it because it didn’t look like the picture.” (Source)
Poisonous Fruit.

“This woman returned a rockmelon (cantaloupe) because she said that it was giving off a radioactive smell. Also she returned some blueberries because apparently they were leaking poison. Yeah she didn’t know that water builds up at the bottom of the packet when you take it out of the fridge. Ever since then I have never doubted human stupidity.” (Source)
The Scratched Tillers.

“When returning tillers (or any yard equipment) and it is scratched all to h*ll with dirt all over it and saying ‘It is not doing what I need it to’ …or you are done with what you needed it for….” (Source)
Something Smells Funny…

“Woman wanted to return some meat she had bought about a week prior, complaining it had gone bad. A dude wanted to return his watermelon because it smelled funny. He handed me a receipt… from a different store. A guy tried to return about $100 worth of meat that had been for a party that got cancelled. We saw him on camera put the meat in his cart, then walk up to the customer service desk to ‘return’ it.” (Source)
Difficult Packaging.

“We have a local store called Bargain Bin that buys lots of returned items and such from other stores. I bought something the other day from there that still had the little return slip taped to it. One of those hard plastic packages that you practically injure yourself trying to open. It had cut marks, stab marks and the plastic was melted in a spot but it was still unopened. Reason returned? ‘Customer did not like the way it was packaged’
It just struck me as funny.” (Source)