"No Rain" by Blind Melon
Not joking. Usually just the opening guitar lines but I sing it constantly, usually while stoned and sometimes I'll even sing it (and yes, I use Hoon's creepy falsetto style). Started a few years ago when I put it on a 90's mix CD for my ex and it doesn't seem like it's going away anytime soon. Eh I like the song well enough so it could be worse I guess.