I'm always surprised at how many people DON'T know how to play Happy Birthday.
In fact, when I was asking around, a friend of mine admitted that he has been caught out by this. He was at a birthday party, there was a piano, and people knew he played.
So they asked him to play Happy Birthday while everyone sang, and he had to admit that he didn't know how to play it!!!
And get this -- it's happened MORE THAN ONCE! Like, wouldn't you learn it after the first time?
So here's the lesson. Don't be like my friend (you know who you are, Scott), and learn one of the easiest songs to play.
The song itself is simple, and there aren't too many problem areas. There is one 'jump' to be aware of, but it's in the key of C and everyone knows the melody.
So that's the easy part...
Now let's get a bit fancy and complicated, and make the song sound 'jazzy'.
The easiest way to do this is to start adding 7ths to the chords. Just make sure the 7th note is still in the key of C.
So if the first chord is a C Major, you'll make it a C Maj 7. If it's a G Major chord, then it will be a G Dominant 7 (because the 7th note is F, not F#).
Try it out, in root position first, and then try adding some inversions in the left hand to really make it sound nice.
And then find out which of your friends or family has a birthday next -- and get ready to surprise them with your performance. Make sure you memorize the song (don't worry it's not long).
Don't be like Scott. Learn Happy Birthday.