I'm sorry, but, have you actually read the AD&D DMG? Because EGG tells you all sorts of things that aren't fun. Acting in character, a la "amateur thespianism" is a good example of something that isn't fun according to EGG and should get kicked to the curb.
I'm sure others with much better knowledge of the AD&D DMG can find lots more quotes of things that I personally find enjoyable in RPG's being called unfun by Mr. Gygax.
Name one, with an actual quote. Gygax tells the reader to do a lot of things, and tells the reader to avoid doing lots of things. But I dare you to find a quote that has Gygax telling you that something *isn't fun* so you shouldn't do it; the closest example I can think of is when he tells the reader that "you cannot have a meaningful campaign without proper timekeeping" which is not the same things as telling them not to engage in anything Wyatt thinks is "boring."