I love fighting him... even the last battle. It kinda makes me cringe inside when stabbing him, though... :/
If I ever met him, I wouldn't dare try to kiss him, just out of immense respect for him, as much as I'd like to. I'd fall to my knees before him and try to be as poetic with my words as possible.
I'd say something like: "Esteemed and powerful Ghirahim, Lord of Demons, Blade of the Demon King, and overseer of the surface world, it is a great honour and pleasure to kneel in your divine presence. I have always dreamed of meeting you, my Lord- your exploits are legendary. I humbly offer my greetings to you, and ask if there is anything I may assist you with. An honour indeed, to serve the Demon Lord."
...because I'm a suck-up like that. Hopefully, I would be playing my cards right and he'd quite like the stroking of his ego.