If I had to choose one post from this thread to best summarize what "looking American" means, it would be this one.

There have been multiple instances where I have been outright embarassed to be classified under the category of American. An individual wearing a t-shirt with "Major League Infidel" printed on it in Dubai, for example. Another example that Proudelitist gave, is the uber tribalistic sub-category. Traveling through the Middle East and Europe, these individuals stand out like a flashlight in the night.

And then there is...best way I can describe it is the obnoxious American sub-category. One of the best examples I have of this is when Mrs. CoolTRVLR and I were waiting for our departure gate to open in FRA. There was an individual meandering around the terminal, and as if his over-sized white t-shirt and basketball shorts weren't already a give away, he was rapping quite loudly with his Beats by Dre headphones on (I could hear him pretty clearly from approximately 25-26 meters away). I do my enjoy my fair share of rap, but I don't expect everyone in my vicinity to want to listen to me rap as well.

I agree with the mindset that the whole "Don't be a terrorist target" with respect to fashion is ridiculous. If a bad actor is intent to do harm, he/she is going to find a target, regardless of what the target is wearing.