I don't know if in Ireland happens the same thing, but at least in Spain and Italy all gays LOVE Eurovision, and many would even go to Sweden or whatever country is celebrated to see the Festival live, all the gay boards are full of Eurovision posts and comments, bitching about this or that country, etc... Some gay pubs celebrate a special eurovision night, with screens and flags and stuff, so everybody can watch the festival live.

Is there a rational explanation for this behaviour?

It's camp and cheesy and poppy and with just the right dash of tragic. Everything gays love.*

*not all gays love these things, obviously. But a lot of them do.

Gorgeous men?

I know one gay guy who wets himself at the thought of it, yet has no interest in music. I think it's the half naked male dancers that turn him on.
I never watch it myself.

How can someone have no interest in music?

They don't

I'm gay and a musician, and I've have little-to-no interest in the Eurovision.

Are you the exception that proves the rule?

Deafness?

Even deaf people like dancing.

I might be, I also dislike musicals, I hate glitter anywhere near performance artists,
I don't think disco balls are all that, I think 80's make up and aesthetics neither look cool nor ironically cool (kitch) and I don't believe anything is improved upon with the affix 'glam'.

Deaf people like music - they can feel the vibrations

Yes but not music. Hence I stand over my answer.
Vibrations aren't music really though. They're a by-product of music.

As you could say is the way hearing people interpret sound waves...

Well, for instance, he never goes to gigs, doesn't have cd's etc., and seems only interested in Eurovision and Madonna, again for the boy rides that are on stage with her.

Sound energy is broken up into two over lapping energies;
Percussive energy, which is the bass energy that is felt in your body. Deaf people experiences this just like everybody else, so for example, there's nothing stopping a deaf person going to a night club or a very loud techno gig and dancing. Also in that respect bass heavy music (dubstep, techno, dub and hip hop etc) would be the most interesting to "listen" to as a deaf person.

And Acoustic energy: the stuff that you hear.

So Eamonn while you have the right idea about deafness and Percussive energy, Percussive enegry is considered part of the sound energy (and music), so it is more correct to say a deaf person is not listening to the music, (one doesn't listen to percussive energy, one feels it) but that they are still dancing to the music , not as you say, to a by product of the music.

It's just their dancing to the part of the music you don't listen to, but feel.