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 look them in the eye
7. you don't remember
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. it was actually them but you were thinking of someone else
15. you're in a different area code, not to mention a different state.
16. she's not human.
17. they're on top
18. It's in a different ZIP code
19. you get paid
20. you change the sheets afterwards.