When someone's entire body arches backwards and tenses up because something in being inserted in their ass, they remain locked in this position because if they relax just for a second, the object may go in their ass.
I'm going to jam this stick up his ass and get him in an asslock.
I tried to put my cock in my girl's add last night, I only got the head in when she went all asslock on me.
The act in which one person is suspended in the air with their limbs inserted into 4 other people's ass's forming the asslock.
Hey man man do you want go asslock Peter tonight?
Sure, lets round up the family and lube up.