Well, after several attempts, I realized that the idea for a set of four "emoticon" coasters really wouldn't work.
I successfully made a frowny coaster, but the "mad" one didn't look mad, and I couldn't get my head around how to crochet a "surprised" face when the entire coaster is done in the round..... I'm not even sure I can explain why it didn't work. Suffice to say the attempts have been frogged and re-created into more smilies and frownies!
I did list several sets of the coasters today on my Etsy site. They will be available in sets of 4 coasters -- your choice either all 4 smiley, or 2 smiley & 2 frowny.