Nudity is somewhat expected in locker rooms. Walking down the street of your neighborhood is not expected. The people that will call the cops are not the same people who use locker rooms. I someone (i.e. your neighbor) hates nudity and sees it as indecent, they will not be in locker rooms.
When you are in the locker room and changing clothes, then some nudity is expected and will not be reported. If you stand there masturbating, engaging in something sexual, or taking pictures, that will be reported.
There's always a fine line between nudity and indecent exposure. In the US, avoiding children when naked is definitely important. Here in the Midwest, I imagine most people don't care much if others are naked and not engaging in any sexual behaviors or attitudes. The gray area is always the minority who are quick to take offense and call the police because they can. Then the authorities have to walk the fine line between honoring both the person feeling threatened and the one just hanging out without pants. I don't want to get stuck on the wrong side of stupid interpretations of vaguely written laws and tend to take precautions as a result.
There is an expectation of nudity in a locker room so not an issue. Other than these three cities being nude in Oregon is legal, but a man cannot expose his genitals to a minor, or do anything that can be considered indecent exposure.