Britishisms

I think I'm getting more used to British English these days, but every couple of days something will come along and trip me up.  For example, Brits often use the term 'quite keen on' something.  Now, wouldn't you think that means that they are more keen than if they are just 'keen on' something?  Well, apparently not.  Putting that modifier in front of it actually means that they are LESS keen than if they are 'keen on' something.  Then, I was preparing for a lesson on phrasal verbs and my tutor suggested I use 'tell off'.  I looked at him quizzically and asked, "does that mean the same over here as it does in the US?"  Thinking to myself, "Is this really something I want to teach beginners???"  He said that it meant to yell at and gave me the example of a mother telling off her children.  Um...so, the answer to my question is a resounding 'no'.  Good thing I asked or it would have been a very different lesson!  :)  And, finally, I should have titled my first post from England: "I should have brought more jumpers!"