There's a Buffy the Vampire Slayer episode in season one, where, when reminded that she has to keep her identity a secret, Buffy replies "In that case, I won't wear my 'I'm a Slayer, ask me how' button." And, as I adore the series, I decided to make my very own!
Trace your button in pencil.
Cut out the circle, but give it some extra room around...the circle is just what will be on the front of the button.
Write in your words...be careful to give them enough space. (I always manage to underestimate how much space I'll need for a word...)
Cut slits around the edge of the paper. Make sure you don't cut past the circle you've drawn!
Put double sided tape on the front of the button, carefully stick the paper onto it, and put a little bit of the tape around the edges on the back. Then fold the tabs you made in step 5 over, and they'll stick down.
Flip the button over and touch up any color, maybe make a border. Then, apply a thin coat of clear nail polish over the pin, which will darken it and cause a little bit of bleed with the marker. (I personally liked that about it, because it makes it seem darker, but I could see people not liking it for their own pin.)
And you're done!