OK, my biggest fish keeping pet peeve is that because I'm female some people think I know nothing about fish and that it's really my husband's tanks and not mine I'm buying for.
Even the local bait guy (who I've been buying worms from for two years now) still thinks it "cute" that I take care of such big tanks "all by myself."
It seems like the lfs clerks will scoop out any fish for a guy and ask 0 questions, but I get grilled on tank size, feeding, tank mates, etc.
Last Saturday I bought a Mekong puffer that I've been eying for a year (waiting for a sale!) and the salesman was annoying the heck out of me for like 20 minutes, following me around, asking the same questions over and over. Finally a clerk that knows me stopped him and said look man, she probably knows more than you about that fish.