From Physical Theories as Women:

Newtonian gravity is your high-school girlfriend. As your first encounter with physics, she’s amazing. You will never forget Newtonian gravity, even if you’re not in touch very much anymore.
[….]
2. Special relativity is the girl you meet at the dorm party while you’re dating electrodynamics. You make out. It’s not really cheating because it’s not like you call her back. But you have a sneaking suspicion she knows electrodynamics and told her everything.
[…]
8. String theory is off in her own little world. She is either profound or insane. If you start dating, you never see your friends anymore. It’s just string theory, 24/7.

However, Physical Theories as Men is more elaborate, funnier and geekier:

0. Newtonian gravity is that guy you had a crush on in high school…. To paraphrase Whistler, the helpful demon from Buffy (Season 2): “Newtonian gravity is like dating a nun. You’re never gonna get the good stuff.” You suspect he may have been gay.
[….]
2. Special Relativity …. length contraction has clearly taken its toll.
[….]
7. String Theory is the sensitive, complex emo guy with an impossibly brilliant mind and lots of emotional problems. …. He constantly complains that nobody understands him, and he’s right….
[….]