Forbidden kiss
When two people perform the act of spreading their butt cheeks to allow their anuses to touch.
Me and my girl last night tried the forbidden kiss and our butthole hair got tangled together.
Forbidden French kiss
When two people simultaniously perform cunnilingus and analingus on a woman at the same time
"I was eating out my girl during a 3 way, and her friend turned it into a forbidden french kiss!"