If they come around where I live, I'll shoot them from my window with my G&P WGC Custom M16 (Vietnam). That will probably REALLY scare them. The looks on their faces would be priceless
My tips for you:
1) Learn every detail - where will they meet and "play"
2) Call the cops, give them the info
3) Kick those wannabe airsofters in the balls*
* - or pinch them really hard, they might sue if you kick 'em in the nuts.