When something's REALLY important. The tags "bold," "underline," and "italicize" begin with the letters BUI, hence the term. When someone using BBCode BUIs something, you know shit's about to go down.

to purchase

The amount of money required to buy a spot in a poker tournament. It's also generally your starting amount of money in the tournament.

The state of mind where one is mentaly retarted due to the use of illegal substances.

Operating a watercraft (Boat) under the influence of drugs or alcohol.

"buy" is the dance you do while you download music off the internet.(usually in an illegal fashion.)

When English learners (and those idiots who don't want to learn) want to say "bought", which is the past tense of buy.