I, of course, wore my FreeBSD "Daemon Crossing" golf shirt to the event. I don't think anybody noticed. I also pretended it was Grand Theft Auto III and slewed the car semi-sideways around the turns on all the up-ramps in the parking garage on the way to the top... sometimes WITH handbrake pulled. I'm pretty fucking sure people noticed THAT, but none of them were mall rent-a-cops, so it's all good. =)
The most amusing bit was getting a free T-shirt - the trainer had a stack of T-shirts, which he informed us he was going to give people for answering questions. The question was "why couldn't you connect Outlook to Exchange over the internet before Exchange 2003", and my answer was "because Outlook and Exchange needed completely unfirewalled network access because they communicate using NetBIOS and all sorts of really nasty RPC calls." Me, I'd assumed that they must have implemented a new protocol that DIDN'T require RPC calls just to read your fucking mail in the new Exchange... but, um, no. Turns out they just built tunneling RPC over HTTP into the new Outlook and Exchange, which the suddenly rather disconcerted instructor explained as he acknowledged that, yes, I'd hit the nail on the head, and tossed me a T-shirt.
As of when P33t and I bolted - after a little over two hours of seminar - that was the only T-shirt he'd given out, and he gave it to me for trash-talking Exchange. Leet. =)