Always when stopping on or turning off something other than a low speed city road, and often in the city.  I've seen quite a few accidents caused by folks daydreaming and not noticing someone slow down or stop in front of them. I'm not going to let them hit me even if I'm in the right.  Sounds like your friend didn't signal and slowed down too fast for the b train to stop (might've been because the driver didn't notice for whatever reason til it was too late or your buddy stomped on the brakes because he didn't think there was a big truck behind him).  If someone was signalling to turn right and I was going too fast to slow down, I'd pass on the left if there was nothing oncoming.  If there WAS something oncoming, then it's a judgement call to either rear end the guy slowing down and probably kill him or take the best option and sneak by to the right. Your buddy was lucky either way, and the trucker may've even figured there was no contact at all and didn't want to stop and trade stories while his drawers were dirty.  I doubt he felt the mirror or tin bend, but might've felt the brush guard hit and bend, but might not've if his truck was bouncing on the shoulder when he went around.  If he felt something he definitely should've stopped though.