My favorite support dumbassary involving the river is this: we're doing fine in lane, as long as everybody's there I'm matching/outdoing the other adc in cs. Then my support for no reason walks around into the river, the other duo gets to zone me off the cs while my support walks into the enemy duo from the flank thinking that somehow that will get us a good 2v2 as opposed to him ending up in the middle of the enemy and all their minions in a split position where if we were to go for the stupid fight they could just decide who to engage on.
The usual way this plays out is that I'm pinging the brain dead moron back and position away from the enemy duo to indicate clearly that we will not 2v2, he walks in anyway, dies and then blames me.