X-O the O face on your exes...right?
His new girl makes his old girls jealous. As they are better looking, his older girls open their mouth in astonishment (draw an O face). It’s not this O face. O-face: (http://knowyourmeme.com/memes/o-face)
The use of “ex” and “o” are referring to hugs and kisses (XOXO) often put at the end of text messages between couples. This is important as most of this song is about Gambino’s memories of this girl or how he is on her way to see her/away from her so the only way they can talk is over the phone.
This could also be seen as a reference to Tic Tac Toe, implying his old girl is trying to win him back from his new girl. If this girl draws O’s over his X’s, he can never win.
Another possible reference ‘Bino could be making are the orgasms he has given ex girlfriends before.
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