Maybe that's it, Merlin - the action's going on in the back seat, and that's what the passerby is staring at?
Years ago, in another galaxy, my boyfriend gave me a load of old crapola about going off to 'find himself' (I wasn't aware he'd mislaid himself) - well, he 'found himself' shacked up with my manager's secretary, while still giving me the old story. When I found out how deceitful he'd been, I decided to vandalise his brand-new American limo - a large silver Chrysler. He had been showing it off to our friends (all sworn to secrecy about where he was living) and I was furious over the fact he'd told me a bunch of lies, not that he'd switched horses. However, when I saw the car, I thought it was so nice I couldn't spoil it. I carefully decorated its front bumper with some well-twined small branches, which would take him some time to remove in the morning before work, but at that point I realised how bloody daft the whole business was.