Do you find the term "butter bar" offensive or demeaning?

Never heard it.

No, I feel it is just slang as is calling a pvt a fuzzy

I think it's disrespectful for enlisted to use it...not so much other officers...they've earned the right.

Nope...not at all. Take it with a grain.

I'd rather be a butterbar than a leg! Jk naa I don't care. I care about getting the mission done.

In 1997 I was a Lance Corporal with one deployment under my belt (I thought I was salty, LOL), I was in my early 20s, and stationed at Twentynine Palms, standing in line at the ATM on base.
I saw that the Marine ahead of me was a 2nd Lt, so I saluted, and when he turned around to return the salute, he grinned at me. Here was a freckle faced ginger kid with BRACES. I realized I was saluting a young adult barely out of school. I was saluting a kid.

Later on when I joined the Navy,
My division officer was usually an Ensign, but thankfully they weren't ring knockers (academy graduates), so they knew enough to know they don't know anything. That's where SNCOs come in. Your O1 needs an E6 or E7 to teach her the ropes.
"Butter-bar" may indeed have been meant as a derogatory term, but it's innocuous enough, even the O-1s are using it. But for military discipline to work, there has to be respect for the rank.
No, I don't think O-1 grade officers should refer to themselves as "butter-bar", that encourages subordinates to use it to refer to them as such in their presence, and THAT is DISRESPECT.

What’s the difference between a 2nd Lt. and a PFC??? The PFC has been promoted once!!!

Next thing ya know the E4 Mafia will be outlawed because it sounds to menacing...A lot of butter bars come in with an over inflated ego. My personal favorite was a butter bar that tried to have an E6 fill out his leave papers for him and tried to have the E6 carry the butter bars luggage from the truck to the room.

In my prior life ...In 1987, I arrived to my first Army duty station (I was Infantry then). I was processes in along with with my new platoon leader , a Butter Bar. We walked into the platoon CP, and the LT put his manuals, and bag on the first empty desk he saw. The platoon sergeant Stood up and threw the manuals out of the window. He introduced himself, and his squad leaders. The SFC then told the the LT that he would be following the squad leaders in the bush for a week, and if at the end of the week, he was proficient, he could claim a desk...and the platoon. When the LT protested, the 1SG appeared in the doorway, and that was that. The LT learned to lead, then he was no longer called “Butter Bar”. Different Army back then, but to me it is the natural way of things.

When I was a E5 it didn't move me to be called buck SGT. I was a young buck, learning to lead. Suck it up butter bar.