Pilot must not have liked the kid ... most don't recommend their profession anyone else as a career.

I make a habit of saying hello to crew on United flights, I find them friendliest and I'm familiar with the routine. More importantly, the stop is to ask them to turn on Channel 9 (ATC Broadcasts). If you're seated way in the back of the plane, swimming upstream after stowing your stuff can be difficult so waiting until after you've landed is best. If you board without a crowd or just have a backpack, ask the FA doing the greeting if you can say hello in the cockpit. Sometimes they'll let you leave your bag in the galley right there while you go say hello to the pilots.

Every crew I've spoken to was welcoming and friendly, it was more a matter of timing. By the time passengers are boarding, the "work' is close to complete, so if they are just bs'ing among themselves, they are much more open to chitchat with you.