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3.
A slap upside the back of the head a la Leroy Jethroe Gibbs from NCIS usually done to someone who did or said something stupid.
Don Gibbs slapped after I asked him to shower with him.
by legaykidd May 22, 2009
 
1.
A sharp, upward slap to the back of the head given to someone acting blaringly stupid. Originated from Special Agent Gibbs from NCIS who employs this manuver often.
"Dude, your mom is so hot."
*Gibbs-slap*
"What? Well she is..."
by plataypusIhateyou October 07, 2005
 
2.
Made famous by Special Agent Leroy Jethro Gibbs (Mark Harmon) on the t.v. show NCIS, this is an open-handed slap to the back of the head. This is usually done in response to an act of stupidity. Done in a half-serious way to show power.
Once at work, I was playing Tetris on my computer. When the boss saw, he Gibbs slapped the hell outta me!
by Mr._ December 02, 2009
 
4.
A slap upside the back of the head usually done to someone who did or said something stupid. It was invented by Leroy Jethro Gibbs.
DiNozzo: "An assisted suicide of a suicide bomber whose suicide was before his suicide bombing. It's like how much wood can a woodchuck chuck if a woodchuck could chuck..."
Gibbs gibbs slaps him.
by mcabbyshipper January 17, 2013