It may not seem insulting, but in context and with the people involved it was.
"You have Janis Joplin hair. Why don't you make it nicer, you aren't 6 anymore."

Now, my mother and I have the same hair type. Poofy/ratty when hair dried, and stringy/greasy with product (all before discovering CG that is!)
My mom and I are musical people, (shes played guitar for 40-something years, sings, writes music) and in all honesty, she looks almost EXACTLY like Janis Joplin. Its always been a endearing joke in our immediate family.

One day we were visiting my maternal grandmother, who is to put it nicely a piece of work that we tend to avoid. She said that in regard to both of us that day, and it hit home for my mom more than me because the janis joplin joke has always been an endearment of her musical side, that for years she actually hid from everyone from shyness.. The fact that it hit on her hair was probably secondary, but that one idiotic comment has stuck with me for 10 years. Janis joplins hair fit her spirit, and my mom has incredible talent and spirit that was muted out from years of living with this critical woman.

I AM happy to say that she now plays in a band at the house of blues on a regular basis, "janis joplin" hair and all, and doesn't give a damn either!