It's one of the first taunts I learned - and the one that taught me the "taunt rhythm," the meter and tones that make any song a taunt.
_____ and _____, sittin' in a tree
First comes love, then comes marriage
then comes ____ with a baby carriage
The truly inspired would add on the following:
Sucking his thumb, pooping his pants
Trying to do the boogie dance
and that's not all, that's not all
he's also drinking alcohol!"
Other versions I heard over the years changed the pronouns around - it was usually one of the people from the first section drinking the alcohol, not the baby.
This seems to be one of the rhymes that EVERYONE knows (I understand there's even a Spanish version) - I've even seen it listed as a good rhyme for teaching Christian children in a home school as an introduction to sexuality (since it sets up the "normal" sequence of events: first comes love, then come marriage, then comes the baby).
Figuring out just how old it is is tricky - it didn't start appearing in print much until the 1970s, though by then it was already referred to as an "old" rhyme. A version including the second verse appeared in Texas Monthly (swapping "wetting" for "pooping" and "hula" for "boogie") in 1976, but in the context it seems clear that it was already considered old. A collection called Glimpses of Appalachian Folklore" lists it as a jump-rope rhyme recorded in Maine in 1961, and Western Folklore listed it as being common in California by the end of the 1960s.
What versions did you know? How old is this thing, anyway?