because it means, in effect "you've done your tiny best to piss me off and you have FAILED MISERABLY you pathetic, snivelling loser!"
hey - it's all in the smile and wink you give the victim as you make the gesture
.......... and yes, OldRider, i noticed on our recent trip down south how many motorists over here in west aus also moved over to let us past .... i always give a sort of little left-handed salute of appreciation when that happens and, it seemed to me, my left hand was seldom on the grip during stretches of that journey! good to see!!
Bookmarks