Unfortunately, the "typical" American tourist is viewed as loud and obnoxious by some German people. Try to avoid speaking in a loud voice when in public, especially in public transport. Try leaving your cell phone at the hotel when you go to a restaurant. Do not get intoxicated in public. Be aware that the German beer is stronger than the US versions.
Drinking beer in public (outside a bar or restaurant) is allowed. However, drinking straight from the bottle makes people think you work on a building site :-). Drinking from a can is considered more normal. Drinking beer on the public transport system is forbidden. Amost all restaurants have a liquor license.