This one. 
By the by, I'm not saying there' anything bad about "Rhiannon." It's just that it's not particularly, y'know, cool.
If you were on a date with someone, and "Rhiannon" came on, and they like, zoned out and said, "Shhh... listen," and who knows, maybe she's a tear or something, wouldn't you furrow your brow a bit?
In all fairness, I'd probably do that if anyone reacted that way to any song in mid-conversation. But the Seinfeld episode made fun of how seriously someone can take a song that has been SO thoroughly rammed down the throats of everyone on the fact of the earth for so long. Like, "Desperado" is corny and shit anyway, but someone reacting to it like it's their personal theme song... that's absurd.