I wouldn't be amused. Unless I give permission, or I know you and your not bothering anything, don't touch my vehicles. That goes for anything that is mine. I might not get too worked up over someone leaning on it, since my paint isn't nice, but sitting in it to me is an invasion of personal space.
Woman where I work rolled her Caddy up by my DD and tapped my door with her door. Walked off like nothing happened. I let it go cause I couldn't find any damage, but if it had might have been a little different. (And believe me I wanted to take out her valve stems and tape them to the door handle.)
I pack but I wouldn't show my piece over someone messing with my vehicle. Like others said some properly conveyed words move people fast enough. In this world you can get in too much trouble for anything involving a gun. If someone showed me their gun in a threatening way I might feel threatened enough to pull mine. So best keep the guns down unless your in fear of your life.