Note: I suppose this one is more Gibbs and Tony than Tony and McGee.
Prompt: "cockroach"
"First Times"
The first time Tony headslapped Gibbs was also the first time Gibbs knocked him in the mouth - hard.
During the aftermath, while the two them stared at each other with something akin to shock and disbelief, Ziva and McGee made desperate attempts to act like they hadn't noticed.
"Uh-" McGee tried, while Ziva turned to stare at a wall.
Instead, DiNozzo and Gibbs both spoke at once.
"There was a cockroach on your head."
"Touch me again and you'll be missing a tooth."