To an offer, "I've done stuff. I can make you happy," implying sex, Angel says, "You wouldn't like me when I'm happy." After having with Buffy, Angel lost his soul and reverted to Angelus.
Angel rhetorically asks Cordelia if she knew how hard it is to think straight with a rebar in your torso, to which she says "Yes, I do." This refers to "Lovers Walk" where she was impaled with a rebar.