Unless you are referring to guys under 16, that is not common behavior. Until then they want their friends to know how grown up they are. The telling friends bit is actually much more common among females. And I have never been able to grasp why they would do this. Girls are extremely judgmental of each other, so why give them something to judge you on?
I think they do that because they are young and want to prove to their friends that they are "manly." in other words they are immature and want to show off. I have yet to find a nice guy that is over 21 that tells his friends that he has sex with ___ and when. I think they just need to learn still.
i think when a girl really enjoys it she will tell her friends too because its kind of something to brag about lol.. I know when I first got with my boyfriend I taped it just so I could show my friends how big his dik is lol