have you ever looked at someone and thought to your head, they must be a liberal or conservative
I've never made such an assumption about anyone.
Probably? I mean, I don't randomly bring up politics--kind of a dangerous topic to bring up--and most other people also tend not to bring up politics (someone who brings up politics to a total stranger is a good sign they're not someone you want to get close to), so there are people I know but do not know their politics. So I've probably assumed wrong before without knowing it.
It's usually pretty easy, but there probably have been some surprises, like my mom loving Reagan back in the day.