Desperate Housewives, Season 8 Episode 2

A: Is there a problem, officer?
B: Yeah. You're parked in a fire zone.
A: Oh! Darn the luck, I am. Well, sounds like somebody's gonna be slapped with a pretty steep fine.
B: Yeah, I should write you a ticket.. But if you promise not to do it again, I'll *let you off with a warning.

*let somebody off: You can use this expression when you excuse someone from any responsibility or punish someone lightly for something wrong. For example, he let us off the hook this one time.