Here's a master class in how not to respond to a terrorist incident.
The tweet, which went viral, read: "I confronted a Muslim woman yesterday in Croydon. I asked her to explain Brussels. She said 'Nothing to do with me'. A mealy mouthed reply."
A Metropolitan Police spokesman said: "A 46-year-old man was arrested at his home address in Croydon on Wednesday, 23 March on suspicion of inciting racial hatred on social media. He was taken to a south London police station."
It's far from the first time someone has gotten in trouble in the UK over a tweet. In 2010 a British man was convicted for a tweet in which he joked about blowing up an airport. The conviction was later overturned, but the incident is commonly referred to as "the Twitter joke trial" and served as one of the earliest warnings to social-media users that they should be careful when posting.
At least 31 people were killed in terror attacks on Tuesday in Brussels. Social-media outlets saw an outpouring of grief and sympathy, but as has been the case following other terror incidents, some people have used an attack as an excuse to lash out at the Muslim community.
The arrested man's tweet quickly went viral, spawning dozens of parodies that riffed on subjects as diverse as Donald Trump and brussels sprouts.
One example: Telegraph reviews critic Robbie Collin tweeted: "I confronted a man who was eating a bowl of muesli yesterday in Croydon. He said "mmfflfffmufflrgh". A mealy mouthed reply."