this is the perfect opp to make it crystal clear to this loser that you're the DJ. beat him to the punchlines, talk it up with everyone, hell even neg hit on her HB coworkers, and keep applying your skillz with the girl and he's toast. hate to say this, but if he's hitting on her in front of you though she's the one who needs to take a stand and refuse his sorry @ss. you can't do anything about what she wants to do, and by getting jealous or angry it just makes you look unsavvy and not in control of your cool, both highly unattractive traits that a DJ should learn to discard FAST if he ever wants an HB LTR.
-jlc