Aside from being rather tedious, the collection of stale libertarian-caricaturing one-liners Matt links below strikes me as getting one thing wrong that's not even an attempt at humor: "If Republicans and Democrats are the thesis and antithesis, Libertarians are a synthesis."
Now, I've been known on occasion to use the "socially liberal, fiscally conservative" formulation to explain to the apolitical what "libertarian" means. But if there's one thing about libertarians that is genuinely ripe for ribbing, it's our notorious rigor in extrapolating from a few basic principles. (You know you're a serious libertarian wonk if you laugh at the old joke about two Chicago School economists who spot a $10 bill on the sidewalk: One bends to pick it up, and the other warns: "Wait, don't bother—if it were really there, someone would've grabbed it already.) The picture of libs as borrowing a little from column A (Democrats) and a little from column B (Republicans) to suit our tastes is both wrong as a description of how (I think) most of us develop our views and backward historically—classical liberalism preceded the welfare-state version espoused by modern Democrats. Hence the "classical."
I was forced to IM Karol Sheinin, by the way, to grill her a bit about libs being "Republicans who can't admit it yet, but who don't want to be as noncommittal and bogus-sounding as 'independent,' " Since she's been out drinking with Kerry and me, I wanted at least a "present company excepted." And Karol clarified that she was thinking mostly of self-described libs in Manhattan, which makes a certain amount of sense: Unlike in DC, copping to being a Republican in, say, Greenwich Village is a little like tattooing "child molester" on your forehead.