So you know how in FANG, Fang gives Max a birthstone ring? She doesn't say what month it is, just that it's the current month's birthstone. When I was working on KCCreations' timeline, I guessed that this scene took place in April. (It's springtime and Orion is visible.) The April birthstone is a diamond.
And in ANGEL, Max calls it a promise ring. When I Google image searched promise rings, the majority were diamonds.
I'm not sure why it cracks me up so much, but Fang probably gave his girlfriend a diamond ring. You know, casually, for her birthday.