The flick The Other Boleyn Girl has me thinking about how confusing it can be for guys to deal with their significant other's hot sister.

One the one hand, you can't say anything bad about her because the one person your woman will always be more loyal to than you is her female sibling. On the other, you can't say anything too nice, because she's also the person we feel most secretly jealous of.

When dealing with your girl's sexy sis, here are a couple of tips that can keep you out of trouble:

1. Treat her the way you would your boss's wife: Be polite, friendly, even charming—but avoid sitting too close or getting touchy-feely, and don't make comments about her appearance.

2. Never side against your woman during sisterly-spats, even if your significant other is totally in the wrong. The only correct ringside comment is, "You and your sister have a solid relationship, I'm sure you'll work it out."

3. Always knock loudly on bathroom doors when she's in the house and listen for the sound of a shower running.

4. If sis tells a dirty joke, directs a sexual innuendo your way, or forgets to wear a bra, pretend you are humorless, gay, and blind.

5. Finally, if your better half ever asks if you think her sis is 'pretty', the correct answer is: "That's gross—she's your sister!" Say the word 'sister' like you would "surgical waste" and then promptly exit the room.