As a dps, if I steal aggro there's two ways, if I see I can kill the stuff before it really has chance with me, I do so. If it seems the mob will die slow, like bosses, I ease up and let the tank to get it back, even if it does lower my dps. Having aggro fight with tank doesn't benefit anyone.

If I tank and I see I loose a mob to dps, a mob that's likely dead in one or two more hits I don't chase it. It's nothing to do with passive aggressive "you take it you tank it" but simply the reality that I better keep the attention of the other mobs, the one lost case is practically dead anyway. Especially with ranged dps the melee mobs hardly even reach them in time.