There's commiseration and affinity there, too. People who say they're bad at cooking will still cook. They're lowering expectations. Additionally, you can "check your math." If you say you're bad at math, run some numbers and then check it to find yourself wrong, you also found yourself right - and you can go back and fix it. Saying you're "bad at math" prepays for the time necessary to do it right. The main thing, though, is that nobody uses math. It's a safe thing to say you suck at. Once you're clear of college the only time most people whip out Excel is if they don't have a copy of TurboTax. I think the STEM crowd is uber-defensive about math because they're required to take so goddamn much of it and as soon as they're out in the real world, they rarely use it either.I don't think people say they're bad at math because it's a thing to boast about, it's just a belief that they could never be good at it.