I think it's because Tories were historically far more right-wing than they are today, and even though they are a little more liberal now, some "classic Tory" features are creeping back into Cameron's government. Take the bedroom tax for example, or the "porn" filter which blocks plenty of sites which definitely aren't porn (including ChildLine, the NSPCC and some LGBT advice sites). There are other things too, like the Royal Mail privatisation and what many call the gradual privatisation of the NHS. And then there's Gove, who seems to be bringing about change for the sake of change, without thoroughly thinking through what his decisions will do nor consulting those who actually know what will happen if his changes are enforced. In addition, many people still have horrid memories of the Thatcher era, so that could easily come into play as to why Tories aren't generally liked.
This list goes on. But I don't think bashing political parties is as bad as racism or religious discrimination. Would you be as worried (for want of a better word) if this person said, "But nobody likes UKIP?" Sure, it's not exactly a civilised debate, but look at PMQs - MPs are constantly shouting at one another for their political beliefs: that's certainly not civilised either.
All in all, I don't think it's a bad thing to mock political parties. It should be their job to "win us over," but clearly the Tories hadn't won the support of the people you met in the pub.