I have, but the DJ rule is to not do this. It's tough, especially if you're involved with a flirty girl. I've figured this much out: the name of the game with this DJ stuff is to sway the girls emotions so she wants you so much she's not interested in anyone else. That's when you have a committment. You can't tell a girl how to feel and who to flirt and talk to.
When she sees that you're threatened or weak, she loses interest. You have to be strong and sure of yourself at all costs and then and only then, even the biggest c*ckblocking arseholes will have no effect on how much she wants you.
Trust me, I've figured this out the hard way.
That being said, there are some things that are downright disrespectful. But before you go blaming the other guys and getting pissed, just remember that getting mad only hurts you. Stay in control. If a guy is flirting a little too much with your girl, chances are that she's letting him, a result of losing interest in you. Go flirt with other girls, and even if you get shot down, she won't know it.