Pitching is appropriate, but keep it down to 30 seconds. You can do it, and it's immesely useful for clarifying your business anyway. Here's some tips.

Don't think of it as a sales pitch. Instead, it's "what do you do?" much like someone with a normal day job would say. Say something interesting.

The goal is to have more conversation. The goal is to get a proper meeting another time where you can full-on pitch. So it's not really a pitch, it's a come-on.

Start with listening, to see what they are talking about. If it isn't about new ideas, then barging in won't help you at all.

If you can get them into some light banter, you could then ask an innocent question.

For example, if you want to start a messaging social networking site, you could ask them their thoughts on Twitter, and if Twitter will ever make any money.

That way you can feel out their thoughts on something that is related to what you are doing, so when you approach them later in their comfort zone you have a better idea how to pitch.

If they ask you about your idea, you should be very short in your explanation, and make certain your passion comes out.

But, if they are there to just socialize, then respect that, and get to know them as a person, that can't hurt either.

Before "pitching" them i would spend time asking them what they are looking for and learning about the process.

The more you find out about them the better prepared you will be. Don't just go launching into some proposal. They get enough of that. Ask good questions.