MIASU is the acronym for the phrase "Mark it and Shut up". MIASU was used exclusively on Message Board Help as a generic response when the board was flooded with users believing MBH to be Message Detail 2. While the phrase may have been appropriate for the circumstances (on par with 'Read the F'ing Manual' for games), it was considered to be blatant trolling and was deleted as such by Moderators. MBH users got the hint and ceased its use.
A variant of MIASU was "Mod it and Shut up", said by some users when a Moderator ranted about a board-related issue.