People don't, as you say, have a right not to be offended. But they do have a right not to be harassed. Since Tong was directly tweeting to Barlow's account, and also engaging in some odd, stalkerish behaviour towards a model (claiming he would only stop traunting Barlow if she dated him) I would say that his behaviour is not a free speech issue, but a harassment issue. You might remember that recently a man was jailed for harassing the families of children who had committed suicide in a similar way. Making jokes about a tragedy is free speech. Directly harassing the families of victims of such tragedies, targeting them directly on their own Facebook pages or Twitter accounts, is harassment. What Tong has done is very different to making a sick joke and more akin to bombarding someone with malicious calls or sending poison pen letters - both of which are rightly illegal.