Kate's test, the Transformations (mixed of course with horror, when Kate figures out Carter isn't human.
The final showdown between Kate and Sander!Thing on board the spacecraft had this troper gleefully screaming "DODONGO DISLIKES SMOKE!" (Internally. It was a packed theater.)
She follows it up with turning the element of surprise against The Thing, which had been bashing through walls and crawling through ceilings to get the jump on everyone. It is not only angry with being found out so suddenly and easily; it is showing legitimate fear.
Lars. The man is a walking crowning moment of awesome.