The word 'blood' is still mildly offensive. It used to be a lot more ruder than it is now. You can get away with saying it on telly during the day, I would say. So just in case you're ever on show during the day.
624. 88 English expressions that will confuse everyone (Part 1)
An episode about British English slang and culture, featuring expressions that Brits know but everyone else finds confusing. Here are the first 30 expressions in a list of 88 that I found on independent.co.uk. Includes plenty of funny improvised examples to make you laugh out loud on the bus.