Is it OK to tweet "fire" in a crowded theater?

Evidently not.

Or at least, it's not a good idea to tweet in jest that you'll blow an airport sky-high if it remains closed for snow, so preventing you from visiting your girlfriend.  Paul Chambers of Doncaster, England found this out the hard way, paying a fine of £1000, gaining a criminal record and losing his job in the bargain.  His appeal will be heard before the high court of the UK and his defense has had at least one high-profile fundraiser, but it's all a bit sobering, to say the least.

This lack of humo(u)r on the part of airport security is not new, by the way, nor limited to the UK.  I remember as a kid -- so, ahem, well before 9/11 -- noticing a sign at the airport we were flying out of saying it was a federal crime even to joke about hijacking, bombs and such, and promptly blanching and making a mental note not to make any smart comments to the nice folks by the metal detector.

With that in mind, the remarkable aspect of the case isn't so much that it involves Twitter, though it is one of the first such cases, but that the authorities chose to prosecute for this particular remark at all.  I don't know how often such cases are prosecuted, but I'd guess it's not too often.  They certainly don't seem to make the press much.  I doubt the story would have been less remarkable had Mr. Chambers been brought in for making the same remark in person at the ticket counter.

In any case, caveat tweetor.

[Paul Chambers' conviction was eventually quashed, two and a half years later on the third appeal, the case having attracted considerable attention and celebrity involvement.  It's not clear if his job was reinstated, but according to Wikipedia he and his girlfriend did eventually marry.]