My single best one was when a customer explained to me that his water is really green, and told me he needs a colostomy to eat all of it.
I had another customer a few weeks ago who points in the general direction of about 9 tanks, and says, "I need one of those."
Me: "Which ones are you looking at?"
Customer: "The tri-color. I want a tri-color."
The woman, her husband, and their two monstrous children (who both appeared to be borderline retarded) all four stand directly in front of the aquarium she's pointing at. All four stare at me, and I'm waiting for the son to start drooling any second. Finally one of the parents realises they're all standing directly in front of the aquarium they're asking me to scoop fish at, and they proceed to yell at their sprog and scream for them to get out of the way.
I proceed to open up the aquarium containing tri-color "sharks" and small plecos, and she starts telling me about how there's just so much algae in her tank that she doesn't know what to do about it. I don't even respond, and I proceed to scoop out a plecostomus, and don't even acknowledge her speaking. Then she says, "I used to have one before, but it was the other kind. You know what I mean?"
Me: "Ma'am, we have about 20 species of fish that eat algae in this store. You'll have to be more specific." (we don't have 20 species at a time, but we get in different types of plecostomus all the time)
Customer: "Oh, you know! The other ones!"
I stare blankly at her.
Customer: "You know!" and she holds up her thumb and forefinger estimating the size of the fish she used to have. "The OTHER ones!"
Me: "Oh. Yeah." Anything to get this lady to shut her mouth and leave my store.
At this point in the process I'm about 10 seconds away from vomiting because the entire clan reeks so bad of old cigarette smoke. I'm wondering if they lock themselves in the car and chain smoke with the windows up, or if they found "Stale Smoke" in the cologne aisle at White Trash Mart on sale 5 for $1, and decided they could skip showers if they applied that liberally. The group of them also all four resemble homeless people, based on the condition of their clothing. It appeared to actually be rotting off their bodies.
I bag the pleco and hand it to whichever one was closest to me and start to walk away. I didn't even ask if there was anything else I could do, I didn't even try to smile.
She yells at my back: "Do you have any guppies?"
D$%^. I have to wait on them some more.
Me: "Yes."
Customer: "Are they expensive?"
Me: "I believe they're $3.99."
Customer: "For feeders?!?"
Me: "Oh. Feeders are $0.20 each."
Customer: "Ok, I need some for my goldfish."
Me: "Well. Goldfish really shouldn't be eating guppies. They're vegetarians, not carnivores."
Customer: "Mine really like them."
Me: "It doesn't really matter if they like them, they're not good for them."
Customer: "Then why do they eat them if they're not good for them?" (This with a smart-alec 'I got you there!' look on her face.)
Me: "They're like children and candy. Just because they eat it doesn't make it good for them."
And I proceeded to walk away, abandoning them in the fish department all by themselves. My manager was standing an aisle over chuckling, trying not to laugh out loud. She said she's amazed at some of the people I can deal with.
I also had one person whose child kept trying to hit me in the crotch while I talked to her. I swear I almost smacked the brat. I'm speaking, and this 5 or 6 year old screams, "HEY! HEY! HEY!" and hits me in the crotch to get my attention.