That happens all the time? I've never had it happen to me, and I routinely stop far enough left in wide-enough straight-or-right lanes to let right-turners pass me on my right, and stop in the thru lane to let right-turners use the right-turn-only lane.

However, if I was stopped in the thru lane and a motorist stopped to my right in the right-turn-only lane, but suspiciously like he was intending on going straight, I would wait to see what he did when the light turned green before I proceeded. If he hesitated I would move ahead and merge right - in front of him ("Motorists are like dogs - if you act like the Alpha they'll treat you like the Alpha"). If he moved immediately I would let him go with a friendly wave and smile.

Serge