It’s a reference to homosexuality. Any sexual references that are not utterly formal or medical are considered offensive by someone.

Even “gay” which is popularized and usable in casual conversation is still considered offensive by some people because of its historical aspect.

I'd wager 10% of the words in the english language are used as euphemisms or slang for something related to sexuality by some group.

For example read up on urban dictionary for some random word -- say omelette:

"Slang word for a sexual orgy." https://www.urbandictionary.com/define.php?term=omelette

So that can't be a yardstick -- there has to be some more objective criteria where a word is recognized as truly offensive by a large majority of the population.

I’m not sure that objective criteria will work here. Slang terms about sexuality often encode the bias of the majority and are targeted at humiliating a minority group.

Rather than trying for a universal measure, I think it’s best to leave it up to individuals, letting us all use whatever empathy and context we personally have.