Sit Down & Shut the Fuck Up--that is to say, "Be quiet and say nothing else, for you are a n00b and your input is not welcome." Used in internet gaming, especially in MMORPGs as a way to tell new joins to a guild that all they need to do is shut up and follow SOP.
"We raid from 9pm to 12pm (or later) PST. If you have a problem with that, SD&STFU. All guild members must have full resist gear banked, and be on time with the appropriate gear to 90% of all raids. Think that is unfair? SD&STFU...."
by Bill Marcellino October 25, 2006