We’re back on the puns again, and this one is really terrible. Imagine being excited about your birthday, only to have your boyfriend tell you it will only be celebrated for half a minute. You’d be annoyed anyway, but even more so when you realize that it’s just a really bad joke.
Like all the most annoying boyfriends, he’s decided that the only reason she’s not finding the joke funny is that she’s not paying attention. Bringing it up every time they’re with new people is obviously not going to annoy her at all.