Funny, I see a lot of tourists and travelers, and the only obnoxiously loud and obtusely rude ones I've ever seen spoke European and Asian languages. But we all need a villain I suppose.
Though I've known about the 'loud American' stereotype for a while I never noticed it until recently when I was in Greece. My friend and I were at a small museum in a small town in the Argolid, which naturally was rather quiet. Then a loud group of people entered. At first we could only hear them and I thought that maybe it was a school class or some such thing but it turned out be just one average American family. It was the stereotype fully alive.

Kind of amusing, really.
But it's true that at one point or another all tourists can be loud and obnoxious, e.g. when drinking is involved. My fellow countrymen also have a similar reputation due to their behaviour in places like Mallorca where they just go to get drunk and behave badly.
A few weeks ago, a friend of mine from Vienna came for a visit. He was astonished how quiet Germans actually are because everyone had told him how loud they were. The truth is that we have a lower volume on average for conversations than most Europeans. But the stereotype still has a basis in reality.
At first, I read the title wrong:
I've always been a guy, so I wouldn't know how I'd feel being a broad.
Anyway, I have no idea what the stereotype about Dutch people is. Perhaps that we smoke pot all day, have sex with just anybody and we don't like to spend money.
Well... Nah, I'll restrain myself. I think the constant mocking of the Dutch is a bit silly, anyway.
On young people, I always find the wearing of round neck t-shirts under button shirts a dead giveaway (a European might go for a v-neck t-shirt if they were going to do such a thing).
Not the Europeans I know. I see people with round neck t-shirts much more often. Hell, even the 10th Doctor occasionally wore one.
Bright, obnoxious bank notes are the best kind.
No Shatner on the Canadian bank notes?
Some people abroad seem to think that all Germans are Nazi sympathisers which then leads to weird and disturbing encounters. When I was in Milano, the neo-fascist friends of the guy I stayed with found out I was from Germany and started doing the Hitler salute and loudly saying the few German phrases they knew, all of them xenophobic and racist while we were walking through Milano. I tried to dissuade them but failed due to the fact that I didn't speak Italian and they hardly spoke English. It was the most embarrassing 30 minutes of my life.
Thankfully, this happens very rarely but it seems that you have to experience this at least once in your life. Most people who don't travel all-inclusive have a similar story to tell (usually I win due to the amount of embarrassment involved

).