Basically if you ever play to an audience you need to keep "happy birthday" in your bag of tricks, because it will come up. Fear not, I dusted off some old notes, did a cross check with other tabs on the net (many had parts that I liked but none were enough by themselves...besides, nobody should ever play a tab exactly as someone else has written it! :))
HAPPY BIRTHDAY 3/4 C G C |---------|----------|----------|----------|----------| |---------|-------1--|-0--------|-------3--|-1--------| |-----0-0-|-2--0-----|-0----0-0-|-2--0-----|-0----0-0-| |---------|----2-----|-0--------|-0--------|-2--------| |---------|-3-----3--|----------|-2--------|-3----3---| |---------|----------|-3----3---|-------3--|----------| F(b5) F C G C ~~~~~ |-3--0-----|-------1-1-|-0--------|--8------|----------|------*| |-1--1--1--|-0-----1-1-|-1--1--3--|--8------|----------|------*| |-0--0-----|-2--2--2-2-|-0-----4--|--9------|-0--2--0--|-3----*| |-2--------|-3---------|-------5--|-10------|----------|------*| |-------3--|-----------|-3--------|-10------|----------|------*| |----------|-1-----1-1-|-------3--|--8------|----------|------*|
Here, have a listen to me play it. It's short, mostly in chords, and easily remembered. Only two parts may cause you some frustration: in the first two bars I'm holding a C shape but I bend my second finger backwards to fret the A second fret third string. I do this sort of mini-barre quite often so it comes reasonably natural to me.
The F(b5) chord may throw you - do it as and F barre chord but don't lay your first finger for the full bar, just fret the low 6, leave the top strings un-barred. Then clamp down the barre for the full F in the same measure.
The rest should be easy for a fingerstyler...don't worry about running up the fret board for the last G and C chord if you don't want to; as with all tabs, make them your own!
...oh and make sure you throw in the heavy vibrato on the end note of "And many more..." I love a bit of comedy in guitar playing, it's not easy to put comedy into guitar playing, so anywhere you can do it you should! :)
JAW