This word used by someone to confirm the act said by another person must be done, similar to "Tell her". If said sentence is banked and then not completed then the speaker is a
twat and everyone ignores them until said sentence occurs.
Banks can be revoked, but only by the person whom placed the bank upon the speaker.
It derives from the popular game
show "The Weakest
Link", in which the word 'Bank' is spoken by a member of the
team whom wishes to bank money already gained.
Henry: Would you moonie that car over there?
George: Yeah of course.
Henry: Bank.
George: *Moonies the car*
George: I may as well just get my dick out now.
Fred: Bank.
George: *Gets his dick out*
John: Look, there's that
guy who
never did his 'Bank', let's ignore him forever.