The "H" probably doesn't stand (consciously, that is)for anything, but simply provides extra emphasis for the truly aggravated to express their feelings, and is learned behaviour passed on from one generation to the next...

However, if it did stand for something, I think this is what it would be...

H is a highly significant letter in the alphabet. It stands for the Horizon, the boundary between Earth and Sky, or in other words, the boundary between Flesh and Spirit, Physical and Non-Physical. The geometrical form of the letter "H" (when it's capitalized) is a symbolic representation of the Horizon. The 2 vertical lines establish a frame of reference, between the Yin and Yang opposites, and the horizontal line is the horizon that joins them. That is an expression of our whole reality.

Since Christ himself is the divine being who stands between the world of flesh and the world of spirit, since he is the bridge between those worlds, it is entirely appropriate that this symbol should be placed in the middle of his title as in "Jesus H. Christ". Christ stands eternally at the Horizon between the Worlds.

What could be more beautiful than that? So there ya have it.

BTW, Buddha was also the Christ, and so was Krishna, and White Buffalo Woman, and a host of others...don't think I'm bible-thumping here, because I am not. You are potentially the Christ yourself, as are we all.