One downside of hitching is that it's somewhat illegal, and more broadly, looked upon with suspicion by the law. Laws vary from state to state (the big deal is that you can't hitch on freeways), but generally, if I see a cop, I put my thumb down and try to look busy with my bags.
Yesterday, though, a cop came up while we were unloading our bags from a ride on the side of a road. We weren't doing anything illegal, but he came up and started reading us the riot act anyway. He did it in the worst way -- that way that some cops have that's very antagonistic. He asked for our ID's, and Kat handed over a passport, which he had plainly never seen before. He flipped around the middle pages, where it has stamps from all these random places, and he and Kat have an exchange that goes something like this: "Do you have a real ID?" "This is my ID, it's my passport." "I know what a passport is, I'm not an idiot." Kat reaches out to flip to the photo page for him and he jumps back. "Don't reach out and grab me." Arg. He goes to harass the guy who had given us a ride, and we sit down a feel like shit for a few minutes for having gotten this guy involved with some asshole.
Then a backup car pulls up and we get more worried. Some dude with mirror shades gets out ambles up to us, but it turns out that he's awesome and tells us everything is gonna be fine. A third guy pulls up and we get to chatting while the asshole cop hassles the driver. They're telling us about the music festivals they went to, and they're like "play us a song!" So it turned out fine -- in fact, one of them drove us 20 miles up the road -- but we thought we were gonna get screwed for a bit.
(Bonus story: the only other time I felt like I was in trouble on the road was also when I was not breaking any laws. Some cops pulled up and started hassling me for no reason, and they made it very clear that it was not OK to ask what I was doing wrong. They searched my shit for pot and drove off eventually, but it left me shaking with anger: cops can really screw you over, and they don't have to have a good reason.)