Comment 4 for bug 600134

How about a one-click-button-to-RSVP, which will set your number of guests to 0. Then it'll say "You're coming to this event :) [ I'm bringing guests ] [ I'm not coming :( ]". Where "[ this ]" is a button. Clicking on 'I'm bring guests' will allow you to add extra guests. If you are bringing guests this means 2 button presses.

I suggest adding the smilie faces to the text to encourage positive happy emotions for coming to events (since we all want to encourage as many people as possible to come). I also suggest a big gap before "I'm not coming" to prevent accidental button clicks (cf. Fitt's Law).