The word derives from the word 'Yemmen' used to abbreviate the words, 'Yeah man.' Yebbi is typically used between two bffs where one bff already calls the other bee and rather than saying, 'Yemmen' he/she is able to say 'Yebbi' which is a shorter form of the words, 'Yeah Bee.' or 'Yes bee.'
Jen: Do you still want me to call you tonight?
Mary: umm... YEBBI!