A blonde, a brunette, and a redhead all work at the same office for a female boss who always goes home early.
"Hey, girls," says the brunette one day, "let's go home early tomorrow. She'll never know."

So the next day, they all leave right after the boss does. The brunette gets some extra gardening done, the redhead goes to a bar, and the blonde goes home to find her husband having sex with the female boss.

She quietly sneaks out of the house and vows to return home at her normal time the next day.
In the morning, the brunette says: "That was fun, we should do it again sometime."