The most resilient gender conventions in roleplaying games?

[Steampunkette]

Worth noting: Most villainous NPCs are male for the same reason most Heroic NPCs are male.

Societal Default.

A Goblin Fighter or an Human Wizard, alignment set aside, are generally presumed to be male. We add the addendum that a character is female as a descriptive element aside from the accepted default.

Similarly, we default to White and Heterosexual in the US. Any black character must be defined by their blackness.

As far as seducing the guard: Political Correctness does not assume or paint men as being controlled by their groin. That is the standard chauvinistic excuse for sexual harrassment or infidelity which is meant to excuse a guy's behavior.

As for men doing the seducing, I'll point you to Zorro, Baron Munchausen, The Scarlet Pimpernel, Jack Sparrow, Don Juan, and a thousand other popular depictions of male seducers buckling more than swashes!

The reasons men don't seduce guards are above. Assumed male gender and assumed heterosexuality.