Culito is basically Spanish for "nice ass" or "sweet ass". "Que culito!" would be "What a nice ass!" or "What a sweet ass!". "Que culito de envidia!" would be something like "What an enviable little ass!", although without the sense of it being physically "little", as in most cases an ass described as a "culito" is probably pretty thick. Oh, and adding the T, making it "culitho" doesn't technically affect the pronunciation, but it means you have to say it with more swagger.

Source: I lived in the Caribbean and spent way too much time watching reggaeton and dembow music videos.