Blow your/somebody’s brains out
Definition 1 of 3
Pro Tip 1/3Violent Imagery
The phrase suggests graphic violence; avoid in sensitive situations. 
His character in the movie was so ruthless, he actually blew his rival's brains out.
Pro Tip 2/3Crime Dramas
Commonly heard in crime-related movies and TV shows. 
In the police series, the detective said he saw too many cases where criminals blew their victims' brains out.
Pro Tip 3/3Informal
Used in informal contexts, it's too graphic for polite conversation. 
When he lost the game, he said, 'I might as well blow my brains out!'