Doesn’t have to be a whole scene - or it can be, if you so desire ;D
It is difficult to choose, I admit, so I’ll start us off with a specific criteria.
MAKES ME HAPPY IN MY PANTS:
No lie, this ENTIRE SEQUENCE, from the shot of Derek’s foot crushing the syringe (HOW IS THAT EVEN HOT, HELP, I’VE TURNED INTO STILES), to literally ROARING at Isaac not to hurt Stiles (SDHAKDSDASAKAKHDLA!!!!!!!!!), to Stiles’ reaction shot after Derek says, all pleased with himself, “I’m the alpha.” HAPPY. IN. MY. PANTS.
Hottest thing eveeeeeeeeeeeeeeeeer. Super!protective!Derek!kink!
(and omg, of COURSE right now I can’t find the exact gifs I want, ugh ugh ugh! I want a Stiles reaction gif! Anyone?)