That's not a very clear definition. Not only because - if we're at schools - the "proper manners" dictated by many are plain r*etarded, making a sin out of the smallest things, but generally it varies what people find offensive and what not. Just think of different languages and cultures. If you ban every offensive word of every living language spoken you will be probably blocked from using words that have a very basic meaning with no harm in your own language.
The staff should be careful when making these rules. For example not every word is vulgar just because it has a*nal in it. (canal, banal, analysis, analogue, should I go on?)
90% of time the player naming his char, specially a 10 year old virgin who perhaps doesn't even know what's a*nal will not think about ensuring to not place it in his name. You could just have a little girl called Ana Louis name her char Analo after herself and get screwed over because of an oversensitive system. (I actually saw such examples happen on other private servers.) Most of the time I see a player banned for inappropriate name, I can't even figure out what was the problem with it. Perhaps I just need a dirtier mind, but I think this whole fuss is needless.
Perhaps they'll make it full blizzlike too and then no one can cry, but I'm personally flattered by the logic of the mature language filter blizz implemented. It scraps out totally harmless words if it recognizes a sequence of letters in it that have a vulgar meaning on their own. (i.eg. mistyping peninsula to penisula)