Much
like your
mom and that's what she said, this phrase has a high potential to add innuendo to a previously-uttered statement. Can also be used to augment a
comeback.
Person 1: Dude, you suck.
Person 2: No, YOU suck. At night.
Girl 1: So, how are things between you and your boyfriend?
Girl 2: Great! I've
never met anyone so awesome!
Asshole 1: At night, that is.
Person 1: I
like chillin' with my homeboys. At night.