First, buy a plain orange top, I got mine from here.
then draw the pattern/face you'd like on the top.
I chose to cut mine out as I'm wearing a tight black dress underneath, but I think it'd be better if you could get a black marker and colour it in as I have a couple of flappy bits. That said I am very much looking forward to wearing it out all day (to work too!) even though my friends said it wouldn't be socially acceptable. Do you have any tips to stabilize the flappy parts? I considered sewing them together but that'd mean the mouth had string in it and I'm not sure if that's the effect I'm going for. Will have to play around!