I'm still concerned some folk thought my avatar was John Peel!?!
I can't say it bothers me massively what people use & the images mentioned aren't pornographic or offensive. An avatar is a personal choice & something that reflects you. If the thing you want to say with yours is "I like this girl", so be it. Perhaps it isn't the most inspired choice? I can try to intellectualise why I've used mine but ultimately it's just a picture of a bass playing hero / influence.
It's your choice to go on a site when you should be working (I occasionally do it too so just an observation, not a criticism) so equally it should be a question of choice for which avatar an individual selects.