Should I apologize to her myself or ask my boyfriend for me?

Ok well yesterday me and my boyfriend were talking on the phone about going to the movies today. As in the three of us. (Me, my boyfriend, and his grandma/guardian.) And he was telling me that we cant go and I was asking why alot And I didn't realize that was why I was (accidentally) irritating him. And I was asking him why so much because we've been waiting for this movie date since last wednesday. That and why the repairman has to come today to fix a sensor for their security system. And when I was asking him why I accidentally cursed and said "Why the f*** not?" mind you this was not intentional at all it literally slipped out. And after that they (temporally disconnected) the phone for the rest of the day and the night last night. And I tried calling him this morning to talk about it and it's still disconnected. And I know they'll turn the phone back on. And now I'm just really wondering if I should call my boyfriends grandma/guardian and apologize myself or wait until my boyfriend gets home and have him tell her I'm sorry for me? What do you think I should do?