That's rich British informal
Used as a sarcastic expression to indicate that someone's fault is similar to yours.
You say I'm so mean? That's rich. You don't even chip in anything.
Jane criticized me for being late this morning. Neither did he. That's rich!
Don't blame it on me! You broke the vase too. That's rich.
1. That's a bit more expensive than expected.
2. That's rather unfair or untrue.
Totally ridiculous.