The Dutch are among the most informal and easy-going people in Europe, and there are not many strict social taboos to speak of. It is unlikely that Dutch people will be offended simply by your behaviour or appearance. In fact it is more likely that visitors themselves will be offended by overly direct conversation. Nevertheless, the standards for overt rudeness and hostility are similar to those in other western European countries. If you feel you are deliberately being treated offensively, then you probably are.
The exception to this openness is personal wealth. It is considered vulgar to for instance reveal the height of your salary, so asking somebody about this will be considered nosy and will probably just get you an evasive answer. Likewise, it’s not advisable to be forceful about your own religion or to assume a Dutch person you’ve met is a Catholic or a Calvinist, since most people do not adhere to any faith at all, and the country has a long, proud history of cultural and religious tolerance. In urban areas it is not considered rude to ask somebody about this, but you’ll generally be expected to be entirely tolerant of whatever the other person believes and not attempt to proselytize in any way. Openly religious behaviour is usually met with bewilderment and ridicule rather than hostility. An exception is the Dutch Bible Belt which runs from Zeeland into South Holland, Utrecht and Gelderland, and consists of towns with many strong Dutch Reformed Christians, who are more likely to be insulted by different religious views. Openly nationalist sentiments are likewise viewed with some suspicion among the general public, though there are a number of nationalistic celebrations like King’s Day (Koningsdag, April 27th) and during football championships. Mostly though, these nationalistic celebrations are mostly used as an excuse to party together rather than being true “nationalistic” events.