Lyric discussion by toaduser 

Cover art for Blue Chair lyrics by Elvis Costello

I don't think this is the original meaning, but certain phrases of the song make me think that the song is about a pair of friends, both infatuated with the same woman, but has chosen one over the other, and the blue chair is a place where they hang out and are still friends.

That doesn't make complete sense, but I think it would be a cool theme for a song anyway.

I think they are talking about a prostitute!

"They're boasting of loving the daylights right out of her in the small hours Down in the Blue Chair You say that your love lasts forever when you know the night is just hours

And still I want her right now Not any minute, hour or day And wherever she is tonight I want her anyway "