Alright, I'm going to confess a dirty secret: the whole "Simmons keeps bitching about weddings, and that's how Grif knows he wants one" comes from idea-for-a-fic-I-will-never-write. The opening of a fic was supposed to go like this: Tucker once joked about being the best man in case these two idiots finally decide to marry, He began to regret it when Grif came to him and said: "Well dude, the time has come. You're my best man and as my best man you're going to help me find engagment and wedding rings". Mind you, that Chorus is still not at the state when jewelry is widely available.
And then the two of them go on some epically stupid quest. At some point Tucker starts to wonder, is this really necessary, why is Grif so sure that Simmons needs the damn rings. So Grif tells hiim all about Simmons' bitching, and Tucker realizes that Simmons is, in fact, a sucker for weddings. And yeah, he absolutely needs the damn rings.