They all saw him do it. Saw him stomp over to where Tony was standing in the middle of the crime scene, and without explanation or hesitation, grab the front of Tony's belt and pull him closer. Saw him efficiently and with practiced ease unbuckle said belt and slip it out of its loops. Saw him make quick work out of separating the knife hidden in the buckle from the leather belt. Saw him drape that now bare strip of leather around Tony's neck. And saw him turn and stomp away with his eyes on the ground without a word. Not a word.
Tony saw what they didn't. He saw the lust in the other man's eyes, saw the pupils dilate and contract. He could see him trying to keep his breath even and steady. He felt the restraint in the man's hands as they were unbuckling the belt, as if to will them not to squeeze and stroke what lived below that belt. And Tony saw the tip of his tongue sneak out from between his teeth as he draped the belt around Tony's neck. Tony didn't need words, he had see it all.
And later, Tony left them all at the office wondering about the events of the day. He drove to a home that wasn't his, only it was. And opened the door that was never locked, to pad softly down the stairs. The other man was there, leaning up against the workbench. And after closing the distance quickly, Tony mirrored the man's earlier actions and pulled him in by the belt. In short order Tony had the man's own buckle knife in hand. The smirk broke widely across Gibbs' face as Tony leaned in for a kiss and teased, “You didn't forget your knife.”