Dave Gorman did a stand-up bit about this. His version goes something like

If you’re happy and you know it and you really want to show it clap your hands

If you’re happy and you know it and you really want to show it clap your hands

But if you’re happy and don’t know it, or unhappy and you do

Then the clauses in this song do not apply to you

But if you’re happy and you know it and you really want to show it

Then, and only then, please clap your hands