Girl math / Boy math definition: what "Girl math / Boy math" means and examples

Girl math is a viral trend where young women explain "flawed" financial logic, such as "anything bought with cash is free" or "if I return something for £50 and then buy something for £70, I only spent £20." It is self-aware and satirical. "Boy math" often mocks different habits, like a boy spending £500 on a gaming chair but refusing to buy a £10 bedsheet. These terms are used to poke fun at the irrational ways we all justify our choices. It is a form of bonding through shared, slightly ridiculous "logic" that everyone knows is technically wrong but feels emotionally right.

Examples:

1. "If I pay for lunch on my card but my friend pays me back in cash, that cash is basically free money. That is just girl math."
2. "Boy math is thinking you don't need a coat in winter because you are 'built different'."
3. "I’m using girl math to justify buying these shoes because they were 50% off, so I actually saved money."