MST 

Mystery Science Theater. When people sit in front of the screen to any movie, the cheesier and more B-grade the better, and make snarky comments.

This can also be done with fanfic by inserting text every so often to point out gross errors in characterization or whatever.

Beavis and Butthead MSTed lots of music videos from their couch.

The Protectors of the Plot Continum MSTed several fics where bad authors had wreaked havoc on canon.

MST by Oinge April 19, 2005

MST 

based off of Mystery Science Theater, MST is a genre of fanfiction wherein the authors of the MST take a piece from another author and taunt it mercilessly

> Jill raised a foot to enter the
> chopper, but was pushed back by the
> soldier.

ARL <soldier>: No shoes, no shirt, no service.

MST by Jon Madden August 5, 2005

MST 

Military Sexual Trauma

The military is too afraid of dealing with MST charges that they are kicking out all the women that report being raped.

MST by TAN22 April 17, 2009

MST 

To parody a la Mystery Science Theater 3000

Honestly, I'd rather sit through a John Agar film festival than another Gonterman story.

MST by Xyzzy February 21, 2004

MST 

Short for "Mary Sue Torture" Usually used in fanfiction. A form of mockery in which an author takes another author's piece, and breaks it up. They generally mock each and every line, pointing out any and all typos and/or grammatical errors along the way.

Work being MST'd: And he carryed her back to merkenwood,
Author MST-ing: O.O I don't even know where to start on that one...

MST by Twitch February 11, 2004

MST 

Stands for MBI Standard Time, a time system used by the MIS Bureau of Investigation. The system sets 13:00 as 0, and adds or removes the appropriate amount of hours for whatever time is being converted to and from MST to other time formats.

Ellie: Hey Big Man! You wanna study tomorrow?
Big Man: Yes!
Ellie: What time?
Big Man: 0 MST.

MST by MBI Official April 30, 2021

mst 

Short for michigans sexiest teens, one of many schools were sexy kids go to learn math science and technology

pick up line: You look like u go to MST.

mst by sexy stud January 6, 2008