I hate when people think they're all that and say 'yow-ie'. Well, basically everyone answered the question.
It's 3 syllables, yah-oh-ee (ヤオイ = yaoi). If people say 'yow-ie', you should tell them off and be a smart :] And if someone tells you therwise, make a bet. Good way to get money haha
Even though this is off-topic, some of my friends are obsessed with anime and yaoi and manga and blah blah (whihc,I personally don't like any of them), and it's funny how I ask them if they're learning Japanese, and they say "I know a little" and I guess the words they know, and it's basically "yaoi" "ai" "oniisan" "kawaii" etc. It's funny. And my friend got mad at me because I corrected her when she said "kawaii" wrong. She said "cow-ah-ee". And i was like "uh... no." and then she's like, I speak American, and I laughed at her. Sorry, im mean XD lol not really... btu yeah
hope that helps lol