social pressure so soon?

Last night Jim, Jonathan and I were at a rehearsal dinner that started at 7pm- Jonathan's bedtime. I was nervous about how he would do with so many new people, loud noises, bright lights, etc so late. But he was wonderful. Smiling, flirting, and generally showing off. Around 9pm we packed up to leave and within moments of being in the car Jonathan was screaming. Not crying or fussing, but screaming in rage and frustration and exhaustion. And this continued almost the entire way back to our hotel. But when we got out of the car and ran into people we knew in the parking lot, he turned on the charm again- cooing, giggling, and being the cutest baby of all time. So either he has decided that he dislikes us and wants to scream at us (but likes everyone else just fine) or somehow he already feels a social obligation to hide his feelings and be on his best behavior for other people. I'm not sure which idea I like less...