Probably a part of me would be excited: like meeting a celebrity. Of course I wouldn't openly show it and I'll try to play some tough poker.
Also, I am probably a bigger threat to the pro than most may believe and it isn't because I am so good at poker (I'd be a pro too if I was at their level), it is because:
- they probably know nothing about me or my play style, but I know theirs.
- one sitting at the table is a very small sample and I could easily get luckier than them, so there is no reason to fear them completely out playing me (unless I'm super obvious/exploitable).
In summary, I'd probably still play my normal game: but my "A game" and enjoy the moment.