The Told-Ya-So

If a fictional woman could become a trucker, that means a woman in real life can do the same!

If someone is there just to prove a political point, they're no more than a Point-Proving Post-It. They don't contribute to the story whatsoever, they don't help the main characters, and no one would really care if they were erased from existence at this very moment.

Point-Proving Post-Its get their name from the Post-It (obviously). A Post-It is a little sheet of paper used to write short messages and post in places such as people's work space and on the refrigerator (hence the name Post-It). A character who is used to convey a short message such as "Told ya so!" or "You're wrong, my political party's right!" would equate to a Post-It carrying out the same functions, only a lot more pointless and annoying.

You see this a whooooole lot in modern TV shows, especially those suspected to have "SJWs"/left-wingers as crew members. However, a Point-Proving Post-It could be used by right-wingers to counteract the messages made by Point-Proving Post-Its of the opposing party or do their own "propagating".

How To Tell Between A Point-Proving Post-It And A Character Who Actually Matters
If you want to do what the header says, ask yourself... If you answered "no" to at least one of these, it's likely the person in question is not a Point-Proving Post-It.
 * "does it turn out this person is really useful to other characters and only happens to go against social norms?"
 * "does this character say/do things a Democrat/Republican typically would?"
 * "would it be like this person to detest things a Democrat/Republican commonly does?"