It's not ok, but I must admit to bristling at it being equated to racism.
There just isn't the same history of horrific oppression.
Fat jokes/fat related bullying /fat insults are not ok but nothing like racism (and we even have evidence that a fat person is less likely to be employed for example).
Same with insults about dress sense, bad teeth, flat chests, big nose, bad skin etc. but none of that is on a par with racism, it doesn't come from the same deep rooted belief that a black person (for example) is less of a human, less valuable, with different morals etc. A person to be feared and therefore oppressed.
Perceived imperfections are easy ways to attack/rib a person. Whether we'd agree that redheadedness is an imperfection is neither here nor there, it's part of a bully's arsenal regardless.
I'm not talking about the effect on the bullied person, I fully believe someone bullied, especially in formative years, can find their whole lives affected by the experience. I'm not trying to minimise the damage.
But the motivation of the attacker/bully is key to whether we're getting into ism territory.
Racial harassment is coming from a fundamental dismissal of a persons humanity.
Insults about hair colour, weight, attractiveness are all interchangeable, the motivation is to hurt/humiliate/embarrass...the victim could be anyone, the insults will be whatever 'imperfection' is easiest to see.