Layover safety is paramount but people take very few precautions.
Personally, I suggest blending in. Watching where you eat and where you drink because you can "disappear" very easily overseas and just as easy in the US.
When you "resemble a pilot" with the dad jeans/khakis and the flip-flops/black shoes, you've just indicated that you're temporarily in town, unsure of your surroundings and an easy target. In Europe, it's even worse because you've just displayed that you don't speak the language, don't know how to contact the authorities, and you'll be leaving soon so you're a SUPER easy target.
Blend in, watch your back, have fun but be suspicious and you'll be fine.