(to be) too big for your britches British Australia adjective phrase
Acting and behaving like you are of great importance, but actually, you aren't
Since he won that grand prize, he has become too big for his britches.
I can't abide those who are too big for their britches.
No one talks to her anymore as she seems too big for her britches.
Conceited or overly proud
Used to refer to a sarcastic person
If something is beneath someone’s dignity, they feel that they are too important to do it.
To prefer talking to listening to other people.
Used to describe someone who is extremely vain or conceited
This idiom refers to being "swollen" with self-importance to the point that one's pants or boots don't fit anymore.