Sometimes humor doesn't travel well. That's the lesson British tourists Leigh Van Bryan and Emily Bunting learned the hard way when a twitter joke got them banned from entering the U.S.

The couple was stopped at Los Angeles International Airport (LAX) last week after authorities found a tweet from Van Bryan in which he said he would destroy America and planned on diggin' Marilyn Monroe up.

3 weeks today, we're totally in LA p*ssing people off on Hollywood Blvd and diggin' Marilyn Monroe up! (sic) Van Bryan tweeted on Jan. 3.

Free this week, for quick gossip/prep before I go and destroy America? he tweeted on Jan. 16.

This did not go over well with officials at LAX.

Van Bryan, 26, and Bunting, 24, told the Sun that they tried in vain to convince the Department of Homeland Security and Customs and Border Patrol agents that they was no terrorists.

Van Bryan explained that the term destroy was British slang for party and that diggin' Marilyn Monroe up was a quote from the animated American comedy Family Guy.

But federal agents were not amused. After passing through passport control at LAX last Monday, the British nationals were detained by armed guards, questioned for five hours, handcuffed, and locked up overnight in separate cells for twelve hours with illegal immigrants and others federal agents deemed as threats. They were put on a plane the next day back to Britain.

Documents provided by Homeland Security explaining the reason for the questioning show a distinct lack of understanding of social media by the agents involved:

Mr. Bryan confirmed that he had posted on his Tweeter (sic) Web site account that he was coming to the United States to dig up the grave of Marilyn Monroe. Also on his tweeter (sic) account Mr. Bryan posted that he was coming to destroy America.

Van Bryan's tweeter account was made private soon after the incident.

The department provided the following statement on Monday afternoon:

Based on information provided by the LAX Port Authority Infoline - a suspicious activity tipline - CBP conducted a secondary interview of two subjects presenting for entry into the United States. Information gathered during this interview revealed that both individuals were inadmissible to the United States and were returned to their country of residence.

According to the booted Brits, the agents even searched their suitcases looking for spades and shovels

I almost burst out laughing when they asked me if I was going to be Leigh's lookout while he dug up Marilyn Monroe, Bunting told the Daily Mail. I couldn't believe it because it was a quote from the comedy Family Guy which is an American show.

It's just so ridiculous it's almost funny but at the time it was really scary, Van Bryan added. The Homeland Security agents were treating me like some kind of terrorist. I kept saying to them they had got the wrong meaning from my tweet but they just told me 'you've really f**ked up with that tweet boy.'

The case highlights an increased surveillance of social media by federal agents and serves as a warning that holidaymakers should never do anything to raise concern or suspicion in any way before traveling out of the country.

Trade association Abta told the BBC that posting statements in a public forum which could be construed as threatening -- in this case saying they are going to 'destroy' somewhere -- will not be viewed sympathetically by U.S. authorities.

In the past we have seen holidaymakers stopped at airport security for 'joking' that they have a bomb in their bag, thoroughly questioned and ending up missing their flights, demonstrating that airport security staff do not have a sense of humor when it comes to potential risk.

The Department of Homeland Security and other federal agencies in the U.S. recently took steps to improve monitoring of social media platforms. The Federal Bureau of Investigation said this month that it's looking for a developer who can create an application to scan and scrape information from a variety of public sites and from government terrorism data.

The app would have the ability to instantly search and monitor key words and strings in all 'publicly available' tweets across the Twitter site and any other 'publicly available' social networking sites/forums (i.e. Facebook, MySpace, etc.)

This social media analysis would be to:

Detect potential threats, develop threat profiles, outline possible courses-of-action, determine timeframe for action by bad actors, identify and develop tactical picture of the location for threat events, and develop intelligence products for counter-measures.

The US Customs and Border Protection Agency said of Van Bryan's incident this week that it tries to maintain a balance between securing our borders while facilitating the high volume of legitimate trade and travel that crosses our borders every day.

We strive to achieve that balance, it added, and show the world that the United States is a welcoming nation.

A welcoming nation, provided you censor your tweeter accounts.