Is It Sexism, Or Not?

If you're not sure if something is "sexist" or not, or biased FOR one sex or not, ~~whether the possible target is male or female, and regardless of the sex of the possible "perpetrators", ~~
switch the target person in your mind to the opposite sex, and see how the situation shifts, or if it doesn't shift.

In other words:  

If you're wondering if a person is getting treated with favoritism by a certain group because they're biased toward their sex, switch their sex in your imagination, but ONLY their sex, and keep everything else about them the same: their gestures, the way they speak, their body language, and what they say. If they were the same person, doing the same things, but the opposite sex, would the group still treat them like they were the best thing since sliced bread? Or would they reject them, or treat them like they're "weird" or "unstable"?

If you're wondering about a group of people being condescending or arrogant toward you, think about how they would treat you if you were yourself, but the opposite sex, in the exact same situation. How would they treat you? Would it be the same, or would they treat you better? Would they treat you with more respect, even though you would have exactly the same experience, knowledge, and capability as you do now, just because you were the other sex?
Watch how they treat others of each sex as well in the same situation.

If you're wondering about a community you happen to be in, or are thinking about moving to, get a good look around before committing to anything. If your son is creative and scientific,, cares about animals and others, with a pleasant, respectful demeanor, and you move to an area where the people are always trying to make boys "prove their masculinity" by acting a certain way, acting "tough", disrespecting girls and women, and shaming them for having any interests outside of a very limited set of preset parameters, he'll probably have to deal with continual childish behavior from other kids, and from adults as well, and he'll probably have a hard time making friends, and receive very little support from adults in the area, if any.
If your daughter plays guitar, loves science, is very creative, and likes to build things, she will likely also get bullied and ostracized as well, by both kids and adults. Which also means they probably won't be safe, because they'll be bully targets and no one will have their back.
Communities that force children into specific and limited gender roles don't like people (or children) who won't follow along with their agenda, so they'll often target them for bullying and/or ostracism. Since it's about control, there are consequences for refusing to be controlled. 
If you find that a group of people you're involved with or have met is treating people with favoritism or disrespect due to a person's sex, then you know that you're dealing with people who have gender-role and bias issues. So if you're the sex that's favored, they'll treat you better automatically, and if you're the sex that's disfavored, they'll be likely to behave disrespectfully and oppressively toward you. This will be the case for your loved ones as well, your children, siblings, parents, and your partner, as well as your friends.
Armed with this knowledge and awareness, you can choose to either use their bias issues to your advantage, or choose to tread carefully, or choose to bow out.  They're not likely to change, or to hear you if you talk about it, because they're invested in ego and belief and constantly reinforcing one another's fantasies and beliefs.
(If you notice, they'll be throwing their own kids, relatives, friends, and own selves under the bus in order to keep their status quo.)
So it's up to you to choose, stay and deal with it, or go.