If I Could Trade Mistakes For Sheep, Count Me Away Before You Sleep
"Thing is, Stiles," Derek says, his voice hard and unfaltering. "I didn't sign up for you. You just hung around until we got used to you being here."
That stings. He hadn't realised how Derek feels about him. They've been getting on quite well, teaming up on little missions and bantering back and forth without malice. Stiles sometimes lets Derek crash in his room after a big fight, trying not to let on how intriguing he finds the werewolf.
"Well now we can get used to you not being here. You're a liability, Stilinski. You can't protect yourself and we always end up having to help you when we've got more important things to do. You're out of the pack."
or
The one where Derek is a terrible Alpha and Stiles ends up walking into a big pile of shit.