The definition of be banging one’s head against the wall is:
(adjective) to continually try the impossible
The young boy was banging his head against the wall because his mother wouldn’t buy him an ice cream cone.
Daughter: I want to go on a date with Bobby!
Mom: You’re too young! You’re only 15 years old!
Daughter: I don’t care!!! I want to!!! You can’t stop me!!!!
Mom: You can shout until you’re banging your head against the wall, but I’m not letting you go!
The boss was banging his head against the wall because his employees were late and didn’t respect him.
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