I think I'm with Andy on this one... I'd buy the cartoon one alot quicker than I would the nekkid profile chick one... much for the same reason I've also bought tee shirts from the kids' clothing section before. Girls in too tight tee shirts with cartoons on 'em = cute, girls with oversized or too-tight tee shirts with images you might find on the mudflaps of an 18-wheeler = a little desperate.
Guys on the other hand? hmmmm... the cartoon thing *would be* kinda lame, but I think it's pretty clear the shirt associated with the link above is for us gals. Now, if some guy bought one of those shirts in pink and it wasn't all clingy, it would still be pretty entertaining for the "you can tell I'm wearing this as a joke" factor.... the other-- speaking as a girl here and all-- is just kinda screaming "hey, look at me!"
I think it would really just depend on the person wearing it... if they were a bona fide ass, or someone you knew had a pretty robust sense of humour, though.