Usually directed towards a very large or ugly person. Insult used to over exaggerate the size of a person or unattractiveness of someone usually a woman with a large head and bad hair. the mammal wildebeest is a very ugly and large animal.
Also used to describe someone with a large upper body and slender lower body.
"You big-a*s wildebeest "
"No i wouldn't date that big wildebeest
" She looks like a wildebeest, the way her hair is all over the place"