Firing seems like an extreme overreaction at the very least, although if this were part of a pattern of behavior, or if the guy were otherwise marginal, I could understand it (even in cases where I wouldn't agree with it). More severe action might also be warranted if the employer were government or some other special cases where even the hint of sexism were a problem (e.g. a rape crisis center employee or something) -- but not a shitty game monetization company.