Stugots is a derivative of 'stu cats' which is Napoletano (dialect from Naples) for "questo catso".
Literally this means "This cock" or "This dick". This expression tresses doubt, disbelief and nothingness. Unlike some translations available on the net, Stugots can't be used as an adjective.
Stugots is often used by Toni and his paesani in "The Sopranos". Toni is from Avellino which resides in the "Campania" area of southern Italy. Most people speak variations of the "Napoletano" in that area.
Chris: Hey Tony, you still owe me 20 grand.
Tony: I owe you stugots!
Chris: I told Carmine I'd go to his daughters wedding, HA! Stugots that I'll go! I'll be laying in the sun at Miami beach instead.