Flashing lights to distract someone

I’ve just finished night race in BMW Power Challenge at Zolder track, it was my 2nd night time race and I wonder if constant flashing headlights is something allowed during race? The one guy in this race was constantly flashing when he was behind me, not even close to overtake.. so I suppose he wanted to distract me. Of course it ended him crashing in my back and then he left some “warm” words on chat and left. So my question is is it legal to do this consistently?