"Do me a solid" means doing something helpful for a friend. (I'm going off of Urban Dictionary definition, which I assume is accurate).
What would be a good colloquialism to describe the opposite of that phrase? E.g. a friend (someone who you expect to do you a solid) does to you something unhelpful or worse.
Best Answer
There are a variety of such phrases, just as there is a spectrum of severity of the dirty deed. A fairly mild one is he went behind my back:
Or he upstaged me:
A somewhat more severe one is he pulled the rug out from under me:
The harshest one that that springs to mind is he stabbed me in the back: