I've only realised this just now... Thank you comments!

For the people who are not convinced, Toby tweeted & deleted this:

"F.U.N, too, is an acronym.

F is for friends who do stuff together
U is for you and me!
N is for anywhere and anytime at all"

And then Toby replied to his own tweet with this: "@tobyfox Down here in the deep blue sea!"

A screenshot of the tweet can be found here:   / this_is_tobys_actual_twitter  
or here: http://undertale-science.tumblr.com/p...

Here's the original link:   / 666043111089553408