But MC didn't know about the grenades... And even if he did, he would've never allowed her to suicide. You should pretty much know already how MC ticks and he's far from being an idiot.
Idk what you want to curse about. But I'd say you shouldn't curse (just because it's better that way). The rules don't specifically say that you aren't allowed to curse, as long as you don't do it to someone personally (so I guess cursing towards the characters in a manga is fine...). Read 5.1.5. I think saying MC is shit is totally fine. Just don't go overboard.