I once watched Boone as he lobbed frag grenades towards a ghoul. He rapidly tossed 3 or 4, and then the next one, it was in his hand, he started the tossing animation...and the grenade flew backwards to where I was standing behind him, watching. eg, it "slipped" out of his hand.
I'd call that a mishap.
Nah, that's a forseeable consequence of the rash decision to give one's companion explosive weapons. A mishap is when you do that yourself :tongue:.
More seriously, a low Luck can cause increased instances of weapon jamming (also related to said weapon's Condition stat) or misfires. Since all human(oid) opponents also have stats, if their Luck is low they are subject to this as well.