A 21-year-old man has been jailed for four months after posting an invitation to start a riot which appeared on Facebook for 20 minutes.
David Glyn Jones, of Bangor, Gwynedd, told friends: "Let's start Bangor riots", Caernarfon magistrates heard.
The court heard an ex-colleague saw the post and alerted the police.
Jones, who admitted an offence under the Communications Act, did not think it would be taken seriously, his solicitor said.
The court heard that Jones typed: "I don't see why everyone's complaining about the rioters.
"Given the chance I'd love to smash up a police car, wouldn't you?"
The prosecution said the invitation, posted as a Facebook "event" on 9 August, was seen by a woman who had worked previously at a shop with Jones.
She reported it to her supervisor and police were alerted.
Jones told police it was "a moment of stupidity" which he regretted.
Defence solicitor Deborah Tennant-Davies said Jones had apologised for his behaviour.
Here are some facts. First the post was on Facebook for 20 minutes. Secondly there was no looting or rioting in Bangor or anywhere in Wales. So far we have been trying to find a single incident of rioting which can be tied to a Facebook event with no luck.
It seems the ugly side of take social media too seriously is hitting. The west foolishly believed that its technology made the Arab Spring possible. People often said Facebook and Twitter made revolts in Bahrain, Egypt and Tunisia.
These claims are very suspect. But it seems law and courts in England are taking a silly assumption and making a injustice, sentencing people to serious prison times for speech on the Internet.
Once again people in the UK wonder why the United States so dominates the Internet and software space. The United States has the freedom of speech written down in the constitution which provides assurances for firms that they will be safe. Firms that run large web sites based in the UK would find their servers liable to prosecution like this.
Social networks probably don't make protests or riots, but they do make money. But acting this way the UK is working to make sure that social media will be less effective in making freedom in the world, will do nothing to stop riots and crime, and will ensure that enterprises continue to move to the United States.