Passionate sports fans can be some of the meanest and that's certainly the case with fanbases in World Football.
Some fanbases are well known for their offensive, nasty or malicious behaviour.
Whether it's comments or sometimes even actions towards a player, team, coach, referee or opposing fans.
While some of these fanbases have calmed down in recent times their history make them solid candidates for such a list.
In other cases even just one particularly heinous action puts them on the shortlist.
The meaner the crowd the higher the ranking of course.
Here are the 15 meanest fanbases in world football.
These guys just missed the top 20 cut but are still worthy of being noted on a list like this.
ADO Den Haag
A group of fans made quite a furor when, as reported by BBC, a manifesto was released stating the club shouldn't sign certain types of people for their side.
In an attempt to quell the outrage, the group, called Landscrona, hit out at the media (via ESPN Soccernet) for distorting their words.
The damage had already been done though.
Barcelona fans are on this list for providing one of the more memorable moments in 'Clasico' history.
Luis Figo received some special treatment when he returned to the Camp Nou in 2002 in Real Madrid colors. There were words said and objects thrown.
Among a number of things, a pig's head was thrown at the Portuguese winger when he lined up to take a corner.
There's more history to Barcelona fan meaness than that though.
A certain section of the fans known as the "Boixos Nois" have been a more malicious presence in Barcelona supporter ranks since the 1980s.
When you are pinpointed in a poll as having one of the worst fanbases in English football your'e bound to be on this list.
Back in 2007 the Daily Mail revealed the results of a survey containing information on which fans of English clubs are the worst.
The fact that the Chelsea hooligan firm was named the "Head Hunters" brings even more authenticity to the claim.
The club's fans have been in the news recently for their destructive actions. The BBC reported on a clash with Cardiff City fans in 2010.
One feels a sense of entitlement when one is a fan of one of the most historic and famous teams in World Football.
You get that feeling with Manchester United fans and they certainly have no qualms talking down to opposing fans etc.
Though they may have calmed down a bit in recent times, the history of the fans' actions can't be forgotten.
Being one of the teams mentioned as one of England's worst fanbases as per survey results presented in the Daily Mail doesn't help either.
There's plenty of passion in South American Football and Penarol is one top Uruguayan club with no shortage in that category.
Fans of the club have a very mean streak though.
ESPN Soccernet reported on some pretty malicious actions by some Penarol supporters after their team lost to Defensor Sporting in a league game.
As seen in this Sun article, Leeds was voted as the most loathed club in England back in 2008.
The club's performances in the 70s played a part in that and so did the fanbase.
There have also been cases of supporters being banned (via Yorkshire Evening Post) for various periods thanks to their actions.
It's safe to say Leeds fans have done their fair share of dirty work in the world of football.
The passion that Napoli fans have can lend itself to a mean streak.
Napoli's Ultras are especially mean and that was evident when the side met Liverpool in 2010.
Italian police admitted (via the Guardian) that some of the more hardcore Napoli fans searched out the opposition supporters for not too nice reasons.
Red Star Belgrade's more ardent fans, known as the 'Delije', certainly have a mean streak as you can see in the video above.
In 2010 crowds were banned for five home games (via UK Eurosport) after fan violence.
Dinamo Zagreb's most raucous fans are known as the Bad Blue Boys.
PSG fans received a taste of this group's mean streak when they clashed (via Reuters) before a Champions League match earlier this season.
As you can see in the video above PAOK fans can be pretty passionate.
That can lead to moments like those reported by the Daily Mail when the team was set to play Rapid Wien in the Europa League.
A list like this could go on quite a ways. So to fit everybody in there'll be a couple entries like this where rival fanbases are paired together.
These two fanbases hate each other with a passion and pass that hatred on to opponents to at times.
There have been numerous incidents involving both sets of fans.
The Guardian has reported on Rangers fans clashing with police and opposing fans.
Celtic has been no stranger to UEFA inquiries (via theTelegraph) thanks to their fans' actions.
As the Guardian reported the club has even condemned the actions of its own supporters in the past.
Galatasaray fans have a reputation for being a fearsome bunch for their opponents.
When Manchester United was getting ready to play Galatasaray in Turkey the Daily Mail took a look at the side's first visit to the Turkish club's home ground.
Surely enough things were tough for the United players and supporters during their last visit.
When Millwall and West Ham play each there's usually trouble between the fans of each team as was the case in 2009 (via the BBC).
Sections of these fanbases don't save all the animosity for their rival fans and players though.
In October of 2012 Bolton forward Marvin Sordell claimed (via the Guardian) he was subject of racist abuse from Millwall fans.
In another recent event reported by the Telegraph, West Ham fans directed some pretty nasty chants to Tottenham fans during their league encounter.
Lazio has some of the most mean and offensive fans in world football.
Their main rival Roma aren't far behind, but Lazio is at the top.
On Monday the BBC reported that Lazio is being charged by UEFA due to alleged racist actions by their fans in a Europa League meeting.
The club has had similar problems (via the Guardian) in the past when their side has faced Roma.
One thing that is certain is that these fans know how to offend. They've even hurt their own club.
Lazio president Claudio Lotito reportedly (via Goal.com) received death threats before the team's league game against Inter back in 2010.
Why did he receive such threats? Had Lazio won they would have been doing the club's major rival Roma a favour in the title race.