Depending on the situation and the pitch/tone used when said, can mean: Yes!, sure..., (REJOICE!!), I dont know, hell naw, fuck no, (ice breaker), why?, eh... ok, I'm weird and make odd noises....
Starsky: Would you like to get wasted tonight?
Hutch: Meh! :-)
Hutch: I FOUND BOOZE!!!
Starsky: MEHHHHH!!!! :-D (rejoice!)
Starsky: Howd you do on your exam today?
Hutch: ...meh... shouldnt have gone out last night :-/
Hutch: ooh he's a hottie eh?
Starsky: eww... mehhhh :-(