1. they look similar. then it's just a tribute.
2. they're twins
3. it's a threesome
4. it's with a celebrity
5. you spread peanut butter on your balls and your dog licks it off
6. you don't remember
7. you don't look them in the eye
8. you get away with it
9. she says it's ok
10. it's with royalty
11. you can please all of them
12. you have two girls at the same time, so one invalidates the other.
13. you go home afterwards and fulfill your duty.
14. you're in a different area code, not to mention a different state.
15. it was actually them but you were thinking of someone else
16. she's not human.
17. It's in a different ZIP code
18. you get paid
19. they're on top
20. you change the sheets afterwards.