From Hovis' famous bread tagline 'the best of both - white with all the goodness of brown' it can either refer to a sexual partner of mixed race or commonly a girl whose vagina is so tight having sex with her feels as good as anal sex.
Guy 1: Hey did you watch that program on cannibalismlast night?
Guy 2: Yeah! Hey I like eating human flesh, I think!
Guy 1: Dude! That ain't Hovis!!!
Guy 1 walks off...