You went to an ATM and it spit out more cash than you requested.

At your birthday party, which was attended by just 23 people, you discovered that by pure chance one of your guests happened to have the same birthday as you.

you got to slap a giant cat fish called bob who ate your child hood pet?

You ate an apple that had an apple in it!

You opened a gift box only to find another one inside, which had another one inside, which had another one inside, which had another one inside, which had another one inside, which had another one inside, which had another one inside, which had another one inside, which had another one inside, which had another one inside, which had another one inside, which had another one inside, which had another one inside, which had another one inside that had nothing inside (except maybe a note saying how much your friends/family love you. Or a copy of Stacking.).

Your dog gave birth to a healthy litter of puppies.

HB m8

you found an egg inside an egg :)

or your video got million view on youtube, or 10 millions :)

You got a matroska doll and found some money in it?

You got a pay rise?

You met someone that looks like your twin brother.

Your mom cooked you something really delicious?

Happy Birthday!
you finally found the thing you lost for many years

Among your presents was a book that had the same text printed back to back on several sudsequent pages.

YOU KILLED SOMEBODY!

You found something valuable in your food.