When is it alright to initiate displays of affection to your LTR?

Also, any feedback on how I've handled these situations: my girl has always been a flirty, carefree type, and she is also witty and intelligent. She, unfortunately, flirts with other guys around me(we are both in my school musical and this is where it mainly happens, maybe it's just a high school immaturity thing). When I sense her doing this, I simply ignore it and fill up my attention with other things; be it friends, other girls, or rehearsal. I feel that approaching her and talking about it is a pretty pussy thing to do, and I know I am leagues better than the scrubs she is trying to get validation from. So I simply dread. Haven't had much success though. Tips?