Ex girlfriend's name?!?!

One time when my boyfriend and I were having intercourse he yelled out his ex's name. I was absolutely pissed about it. We didn't talk for a couple days after it happened. He apollogized and said he didn't mean to and that it was an accident etc. I'm still pissed now that I'm thinking about it. Have any of you ever had a SO call out an ex's name while having sex with you? I'm just wondering if it's something that has happened to any of you.