My bonny lass she smileth is a famous English madrigal

Madrigal (music)

A madrigal is a secular vocal music composition, usually a partsong, of the Renaissance and early Baroque eras. Traditionally, polyphonic madrigals are unaccompanied; the number of voices varies from two to eight, and most frequently from three to six....

, written by Thomas Morley

Thomas Morley

Thomas Morley was an English composer, theorist, editor and organist of the Renaissance, and the foremost member of the English Madrigal School. He was the most famous composer of secular music in Elizabethan England and an organist at St Paul's Cathedral...

 and published in 1595. It is based on an Italian madrigal, published by Gastoldi in 1591 (see ref 1 and supporting recording). The ChoralWiki gives the following words for the two opening verses.

My bonny lass she smileth,

when she my heart beguileth.

Fa la la la...

Smile less, dear love, therefore,

and you shall love me more.

Fa la la la...

The song was parodied by Peter Schickele (http://www.schickele.com/composition/twomadrigals.htm)
(writing as PDQ Bach) as:

My bonny lass she smelleth

Making the flowers jealouth.

Fa la la la...