It's not the smartest thing in the world to do but it's not the end of the world either. Could you get an infection....yes. Could you have some catastrophe happen like to druggies that share dirty needless....no.
Yes it's dumb, when I was younger I did the same thing a few times. Got away with it, never had a problem, might have been lucky, don't know. Either way, you'll probably be fine, just don't do it again.