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

Nothing offensive about it. It's temporary and you'll soon go silver and laugh about it. We all go through the bottom of the chain of command and get it one way or the other. Remember that people that mess with you, like you. If they don't like you, they'll ignore you.

My first Platoon Leader (God rest his sole) had a sense of humor! He was a Graduate if the Naval Academy and he would laugh when ever I called it CANOE U! I asked him if he knew the difference between a Butter Bar and a PFC? No Farley what’s the difference? A PFC has already been promoted once Sir!!!
That started a friendship from November1983 till he passed away New Years Day 2018. I even stood up at his wedding in 1985. Professional, but saw the humor and didn’t get offended over names!

Isn't that the same as calling a new private a fuzzy? Shit always happened to me. It only motivated me to get my mosquito wings asap. People may make fun of butter bars but I think privates get the worst of it, since they don't get the respect that an officer does. If you can't handle being fucked with because of your rank then you chose the wrong job.

Railroad tracks for Captains?!

That's what they are. They are to learn from Sr. NCO's,and develop their own leadership style.

In the Army they often refer to a newly minted 2LT as a “Shave Tail” and the term harkens back to the days when the army used miles for transport. A new mule had its tail cut off so that anyone around it could see that it was new and thus more likely to do something unexpected. 2LT’s being new, more by reputation than actions also tend to do things unexpected and may need. Little more guidance and patience. Not any more wrong than calling someone a boot private.

Butter bar, shave tail, L.T., not really disrespectful nor demeaning. It's common most NCO's do have pet names for 1st and 2nd LT's. Most is earned.

What I find extremely funny - taking offense at being called Lieutenant.

Sounds like some overpaid private got their feelings hurt

Nope. From an enlisted perspective, it’s acterm of endearment. There will come a day when you’ll look back at those memories with fondness.