I'm fairly tolerant of the BBFC, as unlike in the 80s it seems to actually understand (as a set criteria) "real" violence vs funny violence.
Example not of BBFC judgement but of the spectrum of judgemen (using spacks only one type of head butt)
True romance, where the woman is beaten to a pulp, very gritty.. very personal, very claustrophobic you see bruises and stuff.
Sin city, plasters guy head butts a cop, but he's wearing a face mask (we are desensitised to him being just one of a million, we don't have the austin powers ness of them giving that one henchman a back story, we don'tsee any damage..our hero is just on a charge away from overwhelming odds..in a cleary fantasicall escape.
2 head butts, one of which most of my friends won't watch.
(I'm going to watch grifters on thursday, haven't seen it since i was 12.. the bad dude makes angelica housten wear a rain coat so that whilst he's beating her if she loses bowel control she won't make a mess of his rug.. thats a pretty messed up scene- some younger certifications get around it by having so much implied they are actually vastly more unsettling).
Other examples, black blood used in the japanese bit of kill bill, because red visceral would create too much impact for it to be passed. Or Planet terror where the amount of tomato ketchup flying at walls (what previously was called splat gore horror) is perfectly acceptable because they get the joke, there isn't any deep seated trauma in it and the more they let loose the funnier it is (compared to the needle and eye bit which is just freaky).
I like 10,000 bullets resulting in a dam of blood, I hate to see bruises.. and the BBFC seems (for the last 7 years or so ) to be on the same wavelength.
Remember in the 90s..when people were adding swear words.. just so that things were more adult ..some of the sci-fi then was 18 just because the script writer gots his rocks off saying "^(^" twice.. becuaswe he didn't want kids to watch it (the reverse also being true and violence getting through as long as no sex or swearing etc)..its much saner now..
(that said I still don't understand 12a's or their purpose other than to increase box office receipts..your either old enough to see violence and adult themes like S+M by yourself, either by smuggling yourself in underage, or your not..I got in to see terminator 2 (15) but was turned away from days of thunder (12).. I thank my lucky stars for that..go to IMDB and see how certifications are fairly random, with some countries giving something an 18 others give a pg too

) And every end purchasor ignores computer games certs, (like the industry ignored manga, testical chomping spider genitalia bestial demon sex and thought it was a pg till the late 80s.

)
That all said, I'm sure someone out there is getting cross and saying I'm perpetuating the myth of cartoon violence and that it should have a cause and effect.. but meh..I don't want to see Wile E. Coyote screaming in agony and covered in 4th degree burns in an oxygen tent.