A Guy Calls In Sick One Day

And being a suspicious sort, his boss decides to drive past his house to check on him. When he gets there, he sees the guy in the living room wildly banging a blonde woman with the curtains open.

Furious, he calls the guy into his office the next day. "You told me you were sick yesterday, but I saw you fucking a blonde in your living room! How dare you lie to me!"

The guy replies "I didn't lie to you boss, I really was sick. That was my sister."