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...
 * "does it turn out this person is really useless to other characters ?"
 * "does this person say/do things a Democrat/Republican typically would to support the corresponding party?"
 * "would it be like this person to detest things a Democrat/Republican commonly does to antagonize the opposite party?"
 * "is it flat-out obvious this person doesn't exist for any reason other than to promote a political opinion?"
 * "does this person allude or directly refer to political issues, current or past, often?"
 * "does this person cause the other characters to learn a lesson that supports the "good" political party and/or opposed the "bad" party?"

If you answered "yes" to at least two of these, it's likely the person in question is a Point-Proving Post-It.