Kiss

A kiss is a peculiar sort of human bonding ritual involving (sometimes mutual) oral contact. When properly administered by the correct agent, it can provide an incredibly potent power boost to Transformers, with occasionally unpredictable results.

Transformers in general have a problem understanding the phenomenon, leading them down lines of uncomfortable questioning.

Marvel Comics continuity

Bluestreak witnessed Buster Witwicky and his girlfriend Jessie kissing, and he was very curious as to its function. Buster tried to explain, but his dad was right there and so it wasn't a terribly comfortable situation. Brainstorm!

On Nebulos, Highbrow saw Gort kissing his incredibly hot girlfriend. He assumed it was some kind of data transfer. Ring of Hate!