What kinds of tactics are commonly used to psyche out opponents?

some other tactics include,

cutting off one's ear, making bird sounds, laughing when the opponent makes a move etc..

Last time I brought a gun, they sent me out. Damn, the tactic was winning.

Ok, it works only when you play vs someone from the UK, but if you manage to bring the bishop from your region to the tournament hall and to have this religious authority standing still in geographical allignement with your opponent and Buckingham palace, then you'll pin the poor guy to the chair: you'll win as soon as a toilet break becomes urgent!

I remember opponents, staring hard at me before the game ; and one who was nervous tilting one leg up and down without lifting his foot ( there will be an English word for it, but I could not find it ) and one who was humming the Frisian anthem.

And in  chequers/draughts there apparently is a handicapped champion  ( Alexander Schwarzman ) who unintended nerviously moves his fingers on the table, and an opponent ( Alexander Georgiev ) once complained at the arbiter.

I know how difficult it is to play a blind player or a very young girl or very old lady, but that is not their "fault" , it just influences my play.

What about something in between young girl and old lady.  Would you be distracted or intimidated if you were playing a mature absolutely gorgeous sexually attractive woman (or man, if you swing that way)?

In a word, yes. Also, I doubt I'm the only one: http://www.chess.com/article/view/to-be-named

I played against an attractive girl at a highschool tournament.  It was my junior year.  The game ended in a draw and the team blamed me for not winning after she blundered.  I had tried to set up a trap and in the end it equalized the position.  My senior year, though, I played her again at the same tournament.  I was a pawn down for most of the game, but came back from behind and won the game.  It was very difficult to concentrate throughout those games, though.

Claiming that one's greatgreatgreat.....grandfather was a lizard.

Talking in your Batman voice

Why don't you just try outplaying your opponent? 

kicking them under the table.

Turn the chess board around when they are away from the game.

Leave the game in a winning position. Protip: take the clock with you.

Put a blindfold on your opponent (very successful in combination with a gun for intimidation).

if you're playing an opponent from a different country, you can stand up and start shouting your national anthem.

I have found that the moves I enjoy playing the most, and the moves that most frustrate me are the same: it seems to me that around Class C players like myself tend to go wrong most easily when tactics allow for a piece to be placed en pris with impugnity. Even if there's a path to equality, the shock of that move tends to let people (and myself) go astray more easily than just about anything else. 

That doesn't work.  My voice gets scratchy by the end and my opponent finds it amusing.