No need to apologize, you didn't know. In either case, it doesn't matter whether or not Pulp Fiction is "mainstream".

It does not matter what you think. It does not matter what I think. No amount of condescending comments online can go back and change it, the name "GIMP" has caused problems for people, including me, when trying to use it in professional and K-12 contexts.

The ways I personally learned people took offense at these words were when I was trying to use GIMP in highschool, asking if I could "use the GIMP" for a project. My instructor, a man who was paralyzed from the waist down, understandably thought I was punking him. I wouldn't learn this until later, but the most reasonable interpretation was that I was being a shithead, as many teenagers are.

When I explained "GIMP was like Photoshop but free", while Photoshop was already installed on the computers, you won't be surprised the conversation ended there and Photoshop won out.

It's not just that the name was insulting. In most peoples minds, nothing good is free, and "Free photoshop clone" was right up there with "Here's a prize for the 1,000,000th visitor" or "Download these free mouse cursors".