Pat somebody/yourself on the back
Definition 1 of 1
Pro Tip 1/3Self-Congratulation
Use it when you or someone else did something praiseworthy, to acknowledge success or good work. 
She solved a complex problem and deserved to pat herself on the back for it.
Pro Tip 2/3Informal Expression
It’s a casual phrase, best used in conversational or informal settings, not in formal writing. 
When we won the game, the coach said we should all pat ourselves on the back.
Pro Tip 3/3Figurative Speech
It’s not usually a literal action, but a metaphorical gesture meaning to feel proud. 
After the presentation, his boss told him to pat himself on the back for a job well done.