I got killed by a flash in a 5v5 once. 2 henades got me to 1hp and no armour and some flash managed to hit and kill me. And blackhawks fbg stats are padded so dont believe him.
It definitely can and does happen. Obviously it only does 1 damage so a lot of luck is involved. Or, as Blackhawk did you can just shoot someone down to 1 and then let them kill you with a flash. Smokes work as well FYI.