Well you have to remember there are lots of personalities on the road at any given time you may encounter a hot head, maybe the guy behind you took exception when you cut in front of him thats why reacted that way, daming ganyan na driver na ayaw magpatalo pag kinut mo eh parang natalo sa laro. Either way don't loose your cool unless you have to avoid a fist fight or any physical encounter.

What I do when I encounter a slow driver is I wait for the right moment to speed up and overtake, I may flash my lights or beep a couple of times, but if the car infront of me doesn't speed up well I just wait. I find that more effective than rushing the car in front of you, well in an emergency its a different matter.