As a progressive libertarian, one of the more amusing aspects of living in the USA is how I constantly get labelled as a "liberal" by people who have only just met me and (in most cases) have no real understanding of my worldview.
The real underlying factor, though, is that "liberal" has become a slogan that is used perjoratively in modern America, without any real thought. An example: a few months ago my (ex-)wife and I were holding a discussion with my mother-in-law about one of her relatives. The relative had moved to Boulder, CO. "Oooh, Boulder - that's a very liberal town" she exclaimed. Unfortunately I was not there for that conversation, otherwise I might have been obliged to respond "and what point are you trying to make, exactly?".
The conversion of the word "liberal" into something approaching a swear-word is only one example of the dumbing-down of political discourse in the modern USA. One of the best comments about the debasement of the word popped up today on DailyKos:

The concept of "liberal" has gotten so badly defined, that basically, for the dumbest conservatives at least, the thinking is "If I'm against it, then liberals must be for it." The only liberal they know is the strawman-liberal who exists nowhere but in their imaginations, and these nonexistant "liberals" believe in nonexistant policies, and speak words which no real world liberal has ever said. "Liberal" isn't just a dirty word anymore, it's a whole myth.
I wish that there was a concerted effort to push people into facing their concept of "liberal", and force people to realize that they don't know squat about liberals except what conservatives have told them.

I always adopt that recommended policy, usually with interesting results. One of my work colleagues (who is a lovely guy, but who would probably vote for a tree-stump if it had GOP stencilled on it), described me as "a liberal" over lunch just after we met. When I asked him if he had any understanding of my political worldview, he promptly shut up. These days he avoids the "L" word in my presence. Just the other day another person I had just met announced "I don't have much time for liberals" and wondered out loud how "liberal" I was. I intend to hold an interesting conversation with that person, who will be invited to define "liberal" for me. Most of my attempts to ask that question meet with the sounds of floundering, resulting in either the creation of a caricature strawman of progressive worldviews, or a response that essentially translates to "a liberal is anybody who I disagree with".
In my youth in England, in my primary school playground in the UK, I once heard a fellow pupil using a four-letter word beginning with "c" and ending in "t". When I asked him (quite innocently) what the word meant, he started hemming and hawing, and it soon became clear that he had no understanding of the meaning of the word - he had simply picked it up and started repeating it because it sounded good. That, in a nutshell, sums up the way a lot of people in this country use words like "liberal" - as empty slogans, devoid of understanding, insight or content. To this you can add other equally debased words and phrases such as "conservative", "stay the course" (which is a slogan not a strategy), and "family values", although the last phrase more accurately falls into a separate category that might be termed "coded language" (of which more at some later date).
Next time you suspect words or phrases are being used as slogans, it would be interesting to ask the person using them to define their meaning. At the very least they might be forced to think before speaking....