[Buckeye McFrog]

There is no requirement that you must shake hands or say anything you don't want to during the entire Mass.

True, but you aren't exactly painting a warm picture of fellowship in Christ if someone is smiling and extending his hand to you, and you stand there like a log.

[oh8eleven]

and you stand there like a log.
I stand with my hands clasped in front of me and politely nod.
BTW, another practice I abhor is the raising and extending of hands toward a newly married couple. Embarrassing.