[yurylifshits]

Is it rational to feel happiness?

If someone feels proud, he/she naturally just got a good moment in life. I guess your question was: Is it rational to identify yourself with an external entity in order to feel good/bad when something happens to this entity. The answer is: In many cases it is perfectly rational. E.g. when people start supporting an old soccer sclub that got a breakout success, old supporters refer to new ones as "gloryhunters".

By the way, I am a gloryhunter here as well. One of the four Fields medalists this year (Stas Smirnov) graduated from the same high school and college as I did.