Apparently, beef knows no genre. Nicki Minaj called out Christina Milan for taking the "Pretty on Fleek" phrase she popularized and selling it on T-shirts. "I was waiting on my percentage at the door! *tilts head*" she tweeted. Wayne may have had to play peacemaker between the two Young Money cohorts because it didn't last long, but they are not the first rapper and R&B singer to get into a tiff. Read on.