Given how often the semi-nude famale body is shown in the UK tabloid press and tv, it is hard to believe that 'tits' is taken as very offensive over here. I believe that more offence is taken in the USA, as in the example of their changing 'titbit' to 'tidbit'. The word 'titbit' carries no offence whatesoever in the UK and 'Titbits' was the name of a general interest UK magazine for many years.

'Tits' is only a very mild and slightly comical expletive in UK use. The word 'piss' is more vulgar but can be found in the Bible. It might be heard in the matey environment of a pub, such as "Joe has gone for a piss". It has more vehemence in "piss off" but with less weight than the good old Anglo-Saxon "fuck off".

As regards what the public take as swear words, even 'get stuffed' might be classed as such, yet there is 'stuff' in everything.