I know at least half of Americans think soccer(I'll call it football from now on, I'm more comfortable with that :P) is just for little kids and girls, but no, this is THE deal in Europe.
You think you are pretty crazy about baseball or American football, you haven't seen some real crazy arses in Europe.
Although I'm an American, I've never liked the "American sports". I've supported Manchester United and Bayern Munich since I was a little kid(so I didn't know if I had to be happy or sad when Man United beat Munich in Champions League Final in 1999 :P). I AM one of those crazy arses.
But that's about it, I don't speak any German nor do I have any deep knowledge about England. But hey, one shirt can do wonders. Yesterday I've went to a local bar in Munich with Bayern Munich jersey on, and I knew I belong to the "crowd" the moment I walked it. They spoke bad English, especially the drunken ones, haha, but who cares. We've enjoyed the beer and talked for hours and hours about Bayern Munich and the Germany national football team. I even got to met some cute ladies over there :D And at that moment, I really felt like I'm one of the local folks. A great fun, a night I'll never forget(yes, that means I wasn't drunk, haha)
Think of it like this, if you're from Pittsburgh, everybody loves Steelers. And at a bar, an Asian guy with not so perfect English walks in with Steelers jersey with 86 Ward on. Wouldn't you want to get him some drink and talk to him?
But use caution, you do NOT want to wear certain team's jersey when you are at certain cities. For an example, if you wear Manchester United's jersey while you travel Liverpool, trust me, you will get mobbed, literally.
So, if you are one of those people who actually are interested in some European football, how about you grab your favorite team's jersey?
Haha, I told you it was an useless tip for most Americans :P