I never say "GG." I think it's demeaning, uncommunicative, and worse than nothing. When I am soundly drubbed by a worthy opponent, I like to compose a missive, an epistle, a message. I couch it in somewhat antique terms, but I always credit the winner with, I hope, an amusing and self-effacing message.
This is, of course, in online play. In live play they've usually moved on before I even get a chance to write. However, when I do, I usually compose a short message with the penultimate move; that way I'm sure my opponent sees it.
I wonder if..