Yeah, Buffy wouldn't like this one, but I couldn't think of many more potential couples on Buffy - so Rupert Giles and Joyce Summers.
Sure, Episode 3x06: Band Candy put them together for an episode, but we never got a full-blown romance; for various reasons it wouldn't have lasted, but I'd have enjoyed it all the same, and also we didn't get enough of Joyce in Season 4.
Giles is a father-figure for Buffy; I'm sure she'd have accepted the relationship in the end.