Over the last few years, Twitter users have grown accustomed to thinking of the service as a kind of public graffiti wall, or community bulletin board where random announcements and the occasional joke could be posted at random. But a recent incident in which an Irish tourist was barred access to the U.S. due to an alleged Twitter joke has put the service in a new light.

According to a report in the UK Daily Mail, Leigh Van Bryan, a 26-year-old Irish citizen, had one of his Twitter posts flagged by the Department of Homeland Security before he even arrived in the U.S. for a vacation in Los Angeles. The offending tweet, which Van Bryan referred to as a simple joke, was in response to a friend asking about his upcoming plans. Van Bryan replied via Twitter: "Free this week, for quick gossip/prep before I go and destroy America."

According to Van Bryan, in this context the word "destroy" was UK slang for "party." But despite this explanation, Van Bryan and his traveling companion, 24-year-old Emily Bunting, were held for 12 hours in a holding cell and then formally barred entry into the U.S. and sent back to Europe. According to the report, Van Bryan was also questioned about another Twitter joke referring to "digging up Marilyn Monroe."

But Van Bryan maintains that it was all a misunderstanding, saying, "The Homeland Security agents were treating me like some kind of terrorist. I kept saying they had got the wrong meaning from my tweet but they just told me 'You've really f----d up with that tweet, boy.'"

The report comes several days after Twitter announced of censoring certain tweets based on country-specific speech restrictions, a decision that has . The FBI is also reportedly to more closely monitor social networks like Twitter and Facebook.

Whether Van Bryan's tweet was an ill-conceived joke or not, this anecdote will likely serve as a stark reminder to casual Twitter users, accustomed to posting nearly any kind of message, that there are many eyes watching those messages who may or may not take what you tweet seriously. Perhaps the Twitter honeymoon is over?