Anyone ever hear of a First Sergeant being call “Top"?

I never much cared for the term, but I tolerate it as a part of tradition.

Yep, all the time, however TOP exist at the E-9 level by definition, but TOP is like Chief!

I once heard some junior Marines refer to the 1stSgt as the "First shirt." It didn't go well for them.

In 1972 Army, TOP meant, the "Highest" or "Top" ranking NCO in command within that unit, as per, Company, Battalion , Brigade, and Division.
It was to show Respect, and Acknowledgement to that highest ranking NCO.

Sgt Jason Schaeffer: Yes.

At least as far back as World War II in the Army the First Sergeant was called the "Top Kick", this was abbreviated to "Top". Until fairly recently when the Army, and the Marine Corps in particular, got more formal in addressing NCOs it was acceptable to call the First Sergeant "Top". I guess it is more common now to say "First Sergeant" rather than "Top".

Back in the day, our first shirt was always referred to as Top except in formal, official situations. I always thought calling him Top was sort of a friendly but respectful was addressing our 1SG. We were extremely fortunate that our 1SG was for sure a cut above and man to whom as respect was due. SO, TOP is OK with me. TOP was OK with him as well. How about today's 1SG, How do you feel?

Every 1SG I ever had or knew was called Top until I got to HHC Ft. Riley and the 1SG there was NOT happy about being called Top. Never used it again while I was in the Army!!

Sergeant,
Yes! However it was a term that was SELECTIVELY Used! One of my Old First Shirts would get IRATE and respond "I am NOT a TOP, a TOP is a toy! Do you want to Play with me?" But even when I was a Fill In First Sergeant (All of my First Sergeant Time was FILL IN), I was only referred to as "TOP" by a couple of close Senior NCOs and the Bn CSM. They all only used the Term in private or isolated conversations.

Why would you call a "shirt" a "top"? HA ha. I have heard both actually.