That's a tough one. Something similar to that happened to me while I was at a club in downtown Vancouver. I approached a girl that was with 2 other girls and a dude that was drunk and a little drugged out (more drunk than he was tripping though).
Talked to the target girl, and the guy grumbled something that went like "what the fark is he doing here".
I ignored him, but from that point on, he's been staring at me as I kept talking to the target. I noticed the extra attention he was giving me, so I decided to get his attention OFF me.
So when the target finally asked if I was with anybody, I decided to take full advantage of it by saying I was with 3 other guys and pointed towards the middle of the dance floor.
I purposely raised my voice slightly so the douche staring at me would hear, and used my right hand to point towards the middle of the dance floor to get his attention away from me and on to "my buddies".
That instilled hesitation in the back of his mind, in the sense that we outnumbered him 4 to 1 just in case things turned sour.
I didn't have 3 other buddies out on the floor. I was with a scrawny little dude that was busy talking to another girl somewhere I couldn't see.
Naturally, the douche bag didn't know any better anyhow 
Hope this helps,
Max