Bakasi

A kid was tryin to tell his dad about his mum's bakasi, the following conversation took place;
KID: 'Dad, I saw mum's bakasi' 
DAD: 'where?'
KID: 'at her backside'
DAD: 'can u decribe him?'
KID: 'yes dad, its big, wally,bigger than u dad.'
DAD: 'i c'
KID: 'dad, what do u mean by "i c?"
DAD:' i mean i c the reasons why your mum has been avoiding me, she's been seeing her bakasi boyfriend'
When his mother reuturned, it was a thong of war between mother and father,

duh

I hope no be my name Bakassi u use for this joke

what is bakasi?