A store with a dark/alternative theme aimed at teenagers. Found in most local malls. They sell t-shirts, stickers, buttons, jewelry, and some other stuff.
99% of people are faggots about it, and like to assume that only wannabe emo/scene/goth/punk kids shop there. It's become a catch-all phrase to mean "poseur".
In reality, nobody ever walks into that store and sees nothing but clowns trying really hard to be emo/scene/goth/punk, but just normal people.
Half the people who make a big deal about Hot Topic being a poseur store have bought stuff from them in the past anyway, and a lot are probably poseur emo/scene/goth/punk kids trying really hard to convince everyone else they're for real.
In short, Hot Topic is just a store that sells some pretty neat stuff, and everybody who whines about it being for poseurs is a kneejerking dumbass. Oh, but Happy Bunny is really retarded and unfunny, fuck that shit.
Prima: I went to the mall today. I bought these earrings from Hot Topic---
Secunda: OMFG *DEFCON 1* THAT IS A STORE FOR POSEURS!!!!!!!!!! WHAT IS WRONG WITH YOU???? YOU FUCKING FAKE GOTH!!!!!!!!
Prima: Uh, dude, it's just a fucking store. I'm not a fake goth or a regular goth. What are you talking about anyway, I met you in there last month.
Secunda: SHUT UP YOU FUCKING LOSER, I DO NOT SHOP AT STORES WHERE FAKE POSEURS LIKE YOU SHOP.