I'm pretty certain it refers to the mystifying habit Brits have of making jokes about people with ginger hair. One of the terms aimed at a lot of ginger-haired people is "carrot top".
However, you need to give us more context. Please give us the entire sentence in which the phrase appeared, along with the source and the author.
I'm pretty certain it refers to the mystifying habit Brits have of making jokes about people with ginger hair. One of the terms aimed at a lot of ginger-haired people is "carrot top".
Two things. One, apparently you are not one of them. Two, I vaguely remembered that, but I couldn't be sure. (I have heard " carrot top" used to refer to people.)