"Are those real plants?"
"I like how low maintenance it seems, so peaceful and uninvolved."
"Wow, I've never seen those at PetSmart before."
Better yet, I have found it to be even more amusing/annoying when they answer their own questions:
"Of course, those aren't real plants, right?"
"So you eat them in, like, ramen noodles, right?"
"I used to have some of those just like that when I was a kid."
By far the most annoying, though, is when they insult the hobby and its costs upon my accurate, patient explanation:
"Why the hell would anyone spend $120 on a glass box?" (Ha!)
"That's stupid, $60 for one shrimp?"
"But of course, you don't actually really make any money off of this, right?"
They usually back down when I tell them I make more than my friends who work at restaurants through my website.
"Simplicity is the ultimate sophistication." -- Steve Jobs