Answer:

boner

Answer	Crossword Clue
BONER	Slip-up
BONER	Stupid mistake
BONER	Screw-up

BONER	Big goof
BONER	Big boo-boo
BONER	Gaffe
BONER	Screwup
BONER	Blockheaded move
BONER	Boo-boo
BONER	Faux pas
BONER	Silly mistake

BONER	Cause for a head-slap?
BONER	A bungler might pull one
BONER	Fool mistake
BONER	Foul-up
BONER	Cause for hitting the forehead
BONER	Damfool thing
BONER	Dumb mistake