Miis that have been rejected may express the desire to try again. A determined battle theme plays when this happens. They'll even stop being depressed when you allow them to do this, even if they were rejected a second time.
However, this can backfire horrendously. If the other person doesn't show up, they'll be even more depressed than they were before (i.e. Full Sadness Bar).
On the topic of confessions, it's particularly satisfying when the confessing Mii is victorious against a love rival (or two!).
Whenever two Miis get into an extremely spiteful conflict (represented by flame auras) and a third Mii successfully gets the two to make up.
"I did something good today! I should be proud...and I am!"
Getting Miis of your One True Pairing, or you and your significant other, to become sweethearts, or better yet, to get married.
Buying a Mystery Bag and getting a high-value item out of it, such as one of the interiors that costs at least four-digit dollars or eurosnote or five-digit yen in the Japanese version
Being able to prevent a rare item, such as a diamond or an ammonite fossil, from falling on the floor in the Catch minigame.
Feeding a Mii their super all-time favorite food will cause them to rocket into space while epic music plays in the background.