When two people touch bare bottoms and blow botty kisses.
"humphrey that was a lovely truffle kiss, it made me feel all warm and fuzzy inside..... literally!"
When two people kiss after eating chocolate - in this way the kiss is like a truffle and has a lovely chocolate taste.
"Do you want to truffle kiss?"
"I saw those two kool kats truffle kissing the other day."
"Hershey's chocolate is the best to truffle kiss with."