Re: What would you not tell your wife, or girlfriend.
I'm mostly honest except for with prices of certain things, like drum gear. My wife NEVER checks our balances and such in our accounts so there's a little bit of a 'wifey exchange-rate'. If a cymbal costs $250, then it's $149.00 to the wife.
Or, I use another trick if I feel like telling the truth. Example - I just bought a couple (cheap) overhead mics. They were $100 and if I were to tell her this right off the bat she might become pissed, so I'll completely exaggerate the price and say something like "Oh, they were only $299.00 a piece but they're really good." and she'll flip out. I let her flip out for a few minutes until she lets it all out then I say "I was only kidding, they were just $99." Then I'll show her the recepit and she'll say "Oh, really? Oh, okay." I don't use this one very often lest she'll catch on.