There is some debate about the 12A classification for The Dark Knight.
Given the stuff I recall seeing and reading in my teens, and I turned out ok(ish), I am not certain that there is any real role for censorship ("classification") unless it is for very young children (ie, under 12s).
However, as I am attracted to the idea of keeping teenagers out of cinemas on the sole basis that they are likely to be loud and annoying, the current system suits me for films which are unlikely to hold teenagers' interests.
Ideally, I would prefer these as cast-iron alternatives:
"BT" - Boring for Teenagers
"BTc" - Boring for Teenagers (unless Clever)
"BEp" - Boring for Everyone (unless Pretentious)
This would work just fine.