Why do people applaud themselves?

Hmm. I think it's a recent phenomenon. I'm sure when I watched Crackerjack or Ask the Family as a child, you didn't see this.

I think it comes from American shows. I hate it when people - even though they may have won - jump up and down and scream. It is so puerile. Screams and the whistling from the audience is awful too.

I should think that the warm up guy is clapping so they do it too.
I, too, think it looks odd.

I've often wondered about that!

I wonder if it's almost automatic.

You hear applause and feel compelled to join in!

*decides ... not decided.

Grammaretto - To me it's an expression of glee, delight at getting something right. If I get something right at home (like find the answer to a crossword clue), I will applaud and even jump in the air (if I'm standing).

And what's rude in one person's view is acceptable in e.g. another culture. For example in some African cultures, it is a mark of respect to remain with eyes downcast when talking to someone. We may find it rude if someone doesn't make eye contact whilst talking to us.

I guess what I'm saying is - who decided what's rude?

Yes , strange isn't it. Something to do with me, me, and aren't I clever, I suppose. I always think it looks very silly