I refer not to their respective denotations, as their literal meanings are quite unambiguous. It is the different tone with which each is spoken and written and the purpose for which each is used that has always fascinated me.
Liberals never use ''conservative'' contemptuously.
The word seems oddly resistant to a derogatory connotation. Every once in a while, a liberal may refer to one of the right wing as ''reactionary,'' but the label seems to have pretty much fallen out of use. Conservatives are seen by their detractors as selfish and greedy folks who seek to maintain a wide divide between the haves and have-nots. Their principal mission is to deprive the rich of the well-deserved fruits of their labors by overtaxing the hardworking to subsidize the chronically lazy. Humans seem to thrive on polarity, and our adversarial systems of government and justice are certainly proof of that.