A thumbprint is a method of consuming a massive amount of lsd, where a massive (relatively, compared to a blotter dose) amount of lsd crystals are made into a small pile, pressed on with a thumb, and then the thumb into the mouth.

A thumbprint is, despite the large dose is not at a high enough level to reach levels of toxitiy in the human body.

Eating so much fluff that you cease to exist. it makes you appreciate the stuff a lot more, supposedly.

Some crazy ritual the LSD cult uses to ensure loyalty of it's members. Basically it just means eating a shitload of pure LSD crystal powder so you supposedly can " see the light ", but really this is just so you stay devoted and don't rat. people who've been printed are willing to do life in the pen to protect their acid. pretty creepy shit.

The two indentations on a girls back that look like the place where you put your thumbs when you F them from behind.

Sex act in the same realm of the "Dirty Sanchez" and other named acts/descriptions. A sexual act that occurs when a couple is engaged in doggy style sex. The male inserts his thumb into the anus of the female during vaginal intercourse. When she turns her head around to see what happened, he makes a poop thumbprint on her forehead.

While you are having sex with your partner doggy-style, you insert your thumb into their anus.

The mark left from a bloody dick tip on a girl's cheek, which vaguely resembles a thumb. The blood on the dick tip is acquired from having sex with a girl on her period (hopefully unintentionally).