[header] How to make a mega tic tac toe board [title] Unwrap shower curtain and lay on a flat surface. [step] It may be creased so consider doing this a few days before the party. If you don't have time to " de-crease " it days ahead of time, lay a sheet over the top and apply a warm iron to the sheet. 
[title] Create the tic-tac-toe lines with the tape. [step] You will ultimately have nine boxes with the tape.