Intentional is probably the wrong word. It implies knowing people's internal thoughts which is pretty much impossible.
I think it's intentional feeding when a Yasou goes 12/20 by tower diving absurd odds to get kills. They KNOW it's going to kill them. It's not worth... it's fucking feeding and intentionally doing it. But other people tend to think that it's just what you describe and is only for the random idiot that runs straight into the nexus 50 times a game.
I wish they'd issue more warnings for it at least. My backs really hurting from trying to carry the people who go 4/20/4 and only have kills cause I did everything I possibly could to feed them.