Bum - This is the part of your body you sit on. It might also be someone who is down and out, like a tramp. You might also bum around, if you are doing nothing in particular, just hanging out. Finally to bum something means to scrounge it from someone.
*** - Probably the most famous troublesome word for Brits in the USA. I even fell for it myself when I visited my first US supermarket aged 16 and asked how much the fags were. The lady gave me a horrible stare and pretended not to hear me. Little did she know I thought I had found a business opportunity to make money on cigarettes. Fags are expensive here!