Literal meaning: Because, sweet potato (kamote) is annoying.
Kasi - Because (more like defending or answering something)
Si - it could be a pronoun like he/she or in this case this person/that person
ex. "kasi si John nakakainis" - because John is annoying
Kamote - it's a wild sweet potato (literal) but I think, in this sentence it was used as some kind of a nickname or something to refer to that person
nkakainis (originally nAkakainis) - annoying
I think this is what it really means though:
"Because, Kamote is annoying"
like = That peahead is annoying!