point out the fact that they are really a socialist.
Get them to agree to the Non-Aggression Principle, then point out that they are in favor of policies that violate it.
Hit leftists hard from the "left" and right wingers hard from the "right", don't come across as their opposite, but as a more radical version of them.
Try to tie into views they already hold.
Although, my most common argument is that the State is a bunch of criminals, I can't hold myself back on this point.
I absolutely despise, hate, loathe, and want to destroy it with every ounce of my being, and I can't hide it.
I feel like I have a compulsion to to call them out as the liars, thieves and murderers that they are, any time I get the chance.
Check out the Laissez-Faire Journal at LFJournal.com
"The State is a gang of thieves writ large." - Murray Rothbard