If I told my parents I'm "using GIMP", I will get some very concerned looks.

It's a term often interpreted as derogatory for a group of people. (Disabled people)

you haven't heard about it because it's no longer commonly used (for good reason), but it's there: https://en.wikipedia.org/wiki/Gimp#Other_uses

If it's no longer (commonly) used, then the project has outlasted the name's so-called derogatory status and should be free from concern.

that would ideally be true, but it takes a lifetime for that to happen. (basically until all people who have experienced gimp as an insult are no longer alive)