What you're describing sounds like a difference in mate value. It's a combination of any desirable traits like looks, fertility, resources, or anything else. We might spot an apparent difference in two mate values, but the US doesn't have many rules or norms around mismatched pairs. Other cultures might though, with rules around bride price and such.

Most animals are pretty good about assessing their own mate value from physical and social signaling and tend settle into matched pairs more often than not. There are some cool social experiments that repeatedly prove this out, but I don't have any links handy.

I know a couple where the guy is quite a lot older and less attractive than the girl and guys will legit regularly confront the girl at the bar or at concerts and stuff being like “why are you with this guy” visibly upset

Twist the question:

Do you really care if your partner lives-in instagram "reality" or in what you experience as reality?!

Appearance-based "league" costs: it costs attention, focus, dedication, & resources.

Some care about experience-induced-value, others about appearance-based-value, & it shows.

Had a friend tell me once they lost a friend to modeling: it ate her brain.

Now all she could discuss were makeup & hair.

Was Einstein at the bottom, or the top, of "league", once he'd become a philosopher?

See?

One's values is the basis of "league".

_ /\ _

Yeah. People will notice. People will speculate. Wild differences between people's INTERESTS tend to lead to relationship problems... usually. I think wild age differences are only weird when combined with differences in power and interest. Imo

I think it depends on the context.

Sometimes, friends can say something like this from a somewhat well-meaning place. Not necessarily that they're mad at the situation, but more as a confidence booster to help that friend potentially get out of a bad relationship. (Sometimes this can be done in a bad way though).

Other times, it's a jealousy thing. Like, if a guy sees a woman he finds attractive with some other guy, he might start commenting on how she's "out of his league" (regardless of the other guy's qualities) either because he's frustrated he can't find a partner he finds attractive, or maybe even in hopes of competing with the other guy for the woman. This is mostly a toxic thing and rarely has much to do with how well the couple fits together.

For me, it often just makes me wonder what positive qualities the person might have that make them a worthy partner. As someone who is not conventionally attractive at all and dating someone who is extremely attractive, seeing other couples that maybe aren't an exact match in terms of looks gives me hope and confidence.

As a side note, I've actually had a few well meaning friends tell me that my partner is "out of my league", which was a bit hurtful, but I think they were just trying to be protective.

TL;DR: Yeah, people say it (and mean it) for a variety of reasons. But it's usually not that they object to it conceptually, but more that they have their own biases involved. Don't let it affect your opinions though. There's a lot more to a relationship than just how someone looks (or how much money they make).

Extremely shallow people, and VERY insecure will always care about this sort of thing

Nop. At least not in my experience.

What I learned is that people who do care are the most weird and obnoxious. They are outliers most of the time.

Nope and I don't know anyone who does, at least publicly.

No. Its not something real people do.