It's the two words brave and stupidity bundle together.
It is to make a brave choice, when a lot of people would consider it stupid. Usually when the situation is classified as a "Suicide Mission", many would decline but only the ones with the most bravitity will accept.
General: Our men are pinned down and running out of ammo, we need someone to get there and help them EVAC immediately!
Non-Bravitity Soldier: No way I am going, that's suicide!