0_o Was he like belting it out, or just humming softly to himself? And what was he singing?

Ｉ＇ｍ　ｓｉｎｇｉｎｇ　ｉｎ　ｔｈｅ　ｔｒａｉｎ
Ｉ＇ｍ　ｓｉｎｇｉｎｇ　ｉｎ　ｔｈｅ　ｔｒａｉｎ
Ｗｈａｔ　ａ　ｇｌｏｏｏｏｒｉｏｕｓ　ｆｅｅｌｉｎｇ
Ｔｏ　ｂｅ　ｈａａａａｐｐｙ　ａｇａｉｎ！

I once met a (probably) drunk/high guy on a bus who kept saying one line in French to me. He then claimed (in English) to speak French fluently even though his accent was pretty bad, and he never responded to any of the things I said to him in French. I think he claimed to speak Russian too.