In the 1960 Presidential Election there was a televised debate between Nixon and Kennedy. Nixon's sweating and 5-o'clock shadow worked against him on television.

Go to 7:27 for Nixon's opening remarks.
http://www.youtube.com/watch?v=C6Xn4ipHiwE

General write-up on the election.
http://en.wikipedia.org/wiki/United_States_presidential_election,_1960

"Nixon Moment" was used in the article where I found this video:

http://www.dailyfinance.com/story/media/facebook-ceo-mark-zuckerberg-denial/19501322/?icid=main|main|dl4|link4|http%3A%2F%2Fwww.dailyfinance.com%2Fsto
ry%2Fmedia%2Ffacebook-ceo-mark-zuckerberg-denial%2F19501322%2F

I figured it described Zuckerberg's sweating.

For those who are not familiar with Nixon, here is an explanation of Nixon's "Enemies List."
http://en.wikipedia.org/wiki/Nixon%27s_enemies_list

And his bio here:
http://en.wikipedia.org/wiki/Nixon

'Guess some folks might be tired of hearing about him.

In reply to this comment by marinara:
2 VOTES so far? I guess you didn't have a over-the-top title. I liked just watching zuckerburg, what a character.

Article about the reaction:

http://www.dailyfinance.com/story/media/facebook-ceo-mark-zuckerberg-denial/19501322/?icid=main|main|dl4|link4|http%3A%2F%2Fwww.dailyfinance.com%2Fsto
ry%2Fmedia%2Ffacebook-ceo-mark-zuckerberg-denial%2F19501322%2F