Sapo verde a ti
 

I heard this is a corruption of the first four words of the Happy Birthday song in English. Right?
If so, how do the rest of the lyrics go? I'd like to sing it to somebody that way, if possible.

What a mild version of it!

I suppose it goes

Sapo verde a ti,
sapo verde a ti,
sapo verde querido <insert name here>.
¡Sapo verde a ti!

At least our kindergarten version using "apio verde" goes that way.

Then we grow and start using a much more risqué one:

[it sounds like "happy"] alvesre tu iú ...
(and so it goes)

I've heard it as "sapo verde eres tú", in order to keep the "u" ending, but we don't sing the whole stanza. We prefer a short version of "Las Mañanitas" instead (depending on the people and the environment, the first four verses or the first stanzas). :)