It's one of the most useless starts to any conversation (argument) you'll going to have with your loved one. It's usually after you've botched it, and she's no longer talking to you that you think: I wish it went like...
Her: My bum's too big, isn't it?
You: What do you mean?
Her: I'm not attractive with such a big bum.
You: On what basis are you judging?
Her: Basis? It's too big.
You: (sigh) Do you like women? (Nothing wrong if you're bi. I hope you'd be able to tell me, if you were.)
Her: No, of course not. You know I'm not: we've been married for years.
You: Okay. Just stay with me. So, you don't fancy women, right?
Her. (frown) That's right.
You: So the mechanism to judge if a women is attractive - the size of her bum is attractive - to a man isn't part of your makeup, in any way, right?
Her: (deeper frown) Yeah. I suppose. So?
You: Okay, so again, on what basis do you judge? You can't see the size of your bum through my appreciative eyes. And what's more, I'd bop anyone on the nose that said anything derogatory about your bum, or any other part of you, for that matter.
Her: But my bum is still too ...
Her: Ow! What was that for? (Grin)
You: (Grin) You were warned.