quoting dhok, Deacon, Norman, United States:

Consider the following two sentences I've found as Reddit post titles.

Me [26 M] caught my girlfriend [21 F] of 3 months with another guy a couple weeks ago.

Me [19 M] just ended a friendship [18 F] due to feelings of affection.

Somehow, only the 1s object pronoun seems natural here- "him" or "us" would sound a little odder- and then only when there's something causing a hiatus between the subject and the verb.

Those are ungrammatical on their face. I wouldn't even think their authors were English L1s.

I've also heard "[subject noun] and [subject noun] (verb with a 3s marker)" a lot. I can't find any text examples right now, but only because I don't know how to Google the construction; it's certainly very common in speech.

That's them being treated together as a single noun phrase. I can't say where/when I've heard or seen it recently, but it does occur, frequently when treating a list of things as a single subject.

There's also the infamous "Me and him went to the store", which is the default construction for everyone but pedants by now.

Gods it's been a long time since we discussed this, but the short version is the object pronoun forms are also nouns; I remember that Zompist was a stick in the mud on the issue and wouldn't be convinced (surprise surprise) by any heap of evidence shown to him, I want to say by Radius? My recall of any more details is nonexistent.

Finally, Yatalac has informed me that there is a rule in some northern English and Scottish dialects that all present-tense verbs take the 3s marker unless they are immediately preceded by a non-3s pronoun. Apparently this has been around for a while and is on the decrease due to standardization. I don't know whether it has anything to do with the behavior of American English, though.

I doubt it does, because there were dialects in North America (I'm only familiar with Northwest ones, but it easily could have been more widespread) which generalized -s as a present tense marker; if it was derived from that rule, it mutated, because the most common form I've heard is I's for be-1sg. Note that I've only ever heard this in older speakers, and only very rarely.