It stands for shut the duck up. A clean version of the well known STFU which means shut the fuck up.
"STDU, Cate! I don't care about your bunions
by Moochieface7 July 1, 2019
Get the STDUmug. by Simon Callahan January 18, 2004
Get the STDUmug. Get the STDUmug. Get the STDUmug.