Laughing at vs. Laughing with

Let me tell you of one of my subway experiences from last week.

P was spending the day with me since Josh was at a Yankees game. While we were riding the 6 subway downtown, P (standing across from me) gestured that I should look at the guy who was sitting on my left. Apparently, P found something amusing about this guy's face so I refused to follow the instructions. P mouthed something about being blue and I said loudly, "What are you talking about?!" and he made up something about the moonstone on my necklace looking blue on my navy blue shirt.

Eventually, I gave in and took a seat across from my original one and noticed very quickly (in a non-obvious manner) that the guy who I'd been sitting next to had blue ink smeared on his face. He had some ink on his hand and unknowingly to him, every time he touched his face, he smeared some on. P was highly amused by this and kept staring at blue guy openly with no attempt to hide what he was doing. I felt like I had a child who didn't have any manners.

When we got off the 6 to transfer to another train, the blue guy (who'd been told by his friend that his face was blue by then) also got off and was waiting for the transfer. P wanted to get onto blue guy's car, most likely to continue staring at poor blue guy. I vehemently said that I refused to get on that car and I would not ride with P if he wanted to continue staring at blue guy.

We rode on the car behind blue guy, and P kept trying to look through the windows to catch a glimpse of blue guy during the rest of our ride.