Such as:
If a conservative doesn’t like guns, he doesn`t buy one.
If a liberal doesn’t like guns, he wants all guns outlawed.If a conservative is a vegetarian, he doesn`t eat meat.
If a liberal is a vegetarian, he wants all meat products banned for everyone.If a conservative sees a foreign threat, he thinks about how to defeat his enemy.
A liberal wonders how to surrender gracefully and still look good.
For the rest, visit The Bookworm Room. 
(hat tip: The Anchoress)
Read them on the 
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If a conservative sees a foreign threat, he thinks about how he can use it to further his political agenda.
You could also say
If a liberal doesn’t like abortion, she doesn’t have one.
If a conservative doesn’t like abortion, she wants all abortions outlawed.
The extremes on both sides are equally nutty, and both represent a really small portion of the population.
“If a liberal doesn’t like abortion, she doesn’t have one.
If a conservative doesn’t like abortion, she wants all abortions outlawed.”
Good rejoinder.