Let's face it, lots of colors just don't belong together. Figuring out what colors work and don't work is either basic color theory or you find out by trial and error while working on art. What colors do you not like together in art? I really hate red and green together but that's just my hatred towards the color green in general. Also most colors combined with brown are not my forte unless its a very dark brown and a neon color.
I generally dislike any color (aside from gray) paired with barely-not-the-same color and treated as if that difference should be considered major and contrasting. Mostly this applies to fashion and clothes for me (you will never ever see me wearing blue jeans and a blue shirt), but in visual art it's quite similar. A drawing/painting that's 90% red like some kind of autumnal/fiery/blooded scene meant to evoke a very specific emotion, but some of the red is rather tomato-like and some of it is rather maroon-like and some is rather cherry-like, but aside from just a few details it's all just red, red, red; it will feel distasteful to me. Same with any other color: a large piece of visual art that's mostly one color with only slight variations throughout, it feels sloppy and poorly-thought for me.
I basically dislike any over-saturated colour paired with any other over-saturated colour(because it hurts my eyes), especially if they're contrasting colours(red and green, blue and orange etc.). They just don't work for me.
I think most colour combinations can work depending on how they're used so I dont have a colour combo I dislike to be honest? I think most duo colour combos that make people wince a little (think bright blue and neon yellow) can work adding a third colour to break them up.
Neon green + medium brown has gotta be the most off-putting colour combination in my opinion. Not once have I seen it used in a way that looks pleasing to the eye.
I also don't like red and green. I mean, I do, but I don't like to use those colors together because it makes everything look like it's Christmas. Other colors that I don't like are orange and pink, unless they have a very distinct shade difference, because or else they'll look too similar. I also don't really like dark purple and yellow. Purple and yellow may go together, but I feel like they would have to be similar in shading, otherwise they just contrast way too much.
I know they're supposed to contrast, but I feel like if the shades are too different from each other, then the contrast doesn't look as good.
