The action of tucking your boner into the waist band of your pants.
I was in public when you sent me that pic, I had to Friar Tuck it!
A Friar Tuck is the result of a large man or woman sitting on a dirty toilet. The excess skin will encompass the toilet rim picking up hair or dirt. The resulting line of hair across the ass resembles the hairline of Friar Tuck.
If Grace sits on that toilet she'll have a Friar Tuck two inches thick!
The extremely gay look of only tucking in the front of your shirt and leaving the rest hanging out. Often used to show a "witty" and "humorous" belt buckle that is in all actuality "lame" and "obnoxious."
Tom: How was the frat party last night?
Frank: It was okay, lot of Friar Tucks there though.