Who's the Loser?

A few days ago Craig was out and about.  Coming home a gray Traverse cut him off, then turned into our neighborhood.  Thinking it was me, he made the loser sign on his forehead.  Imagine his chagrin when the car turned right instead of going straight and he realized it was not his mother driving it.  Which leads to a few questions...Why is it okay to "loser" your mom, but not someone else?  And why would I cut him off with my car?  If he hits me I'll have two cars in the shop.