The 42-Year-Old Virgin - S3-E6
Continuity mistake: This episode reveals Stan has never killed anyone, even though he killed Jay Leno in Stan of Arabia: Part 1, killed Jackson's Double in It's Good To Be Queen, accidentally disintegrates one of his co-workers in I Can't Stan You, and shot a hang glider in An Apocalypse to Remember.
Chosen answer: She declines because she is still angry with him for ditching her.