Do you play differently if you know the person?

I've just been looking at my history and my two longest games are with the people I know, indeed friends. Why?
If I just knew them by sight - would that affect my play?
If I dont' know the person I don't try any less - or do I?

I'd be interested if anyone has the same results?
Or has anyone met someone they'd been playing for ages before meeting them?

Mmmmmmmmmmmmmm?

All games are the same for me except when I play against attractive women.

I lose those games.

In blitz chess in coffee shops I play a bit differently against some players.
Like if I know my opponent ignores my moves or fears my moves I can do sacrifices which they should accept {take and chuckle} but they don`t bother to even look at my moves or they assume I have a good reason for sacrificing.
This allows me to accomplish seemingly impossible things since the opponent doesnt accept my sacrifices I can simply put a piece en prise and my opponent won`t take it which allows my piece to miraculously get to a square it wouldnt normally be able to reach.

I play differently if I know which openings he's used to and stuff.

Absolutely. There are positions we have played through, analysis we have talked about, there is a history. I know people say play the board not the person, but its a lot of fun playing the person sometimes 🙂

How can you not? Especially if it's someone you have analyzed games with before.

Absolutely. For instance, against my dad I'll play Caro-Kahn or the French with black, and queen's pawn with white. I play these openings almost exclusively against him.

There is a definite psychological element in any chess game. Of course, if you know the person or even if you have watched them play a great deal you would know what phych-outs will help rescue you from a lost position.