There are too many of these moments in my memory from my old school. We had 3 main people who would ALWAYS say this in ANY circumstance.
We were doing a science project involving a bunch of plastic tracks, teacher watching us closely.
M: Gr. This is just too long and floppy!
R: TWSS!
Teacher:...?
Class: *Laughing*
Teacher: Quiet!
There were a million of these, and most were rather lame, but you can only guess what people are going to make into a TWSS moment.