Season 7, Episode 7: "The Secret Code"

Not ringing a bell.

When my uncle said to him, "The president's been shot"...

...Oswald winked at him and said, "I'm gonna go catch a movie."

Right when we were in front of the bathroom door.

The bathroom door.

I remember someone had played tic-tac-toe on it and the X's won.

They went diagonally from the top left to the bottom right.