Many Folk Songs are bawdy or contain innuendo. Most are not explicit but make it obvious what is intended.
Good examples include The Cuckoos Nest, The Bonny Black Hair, Hares on the Mountain, The Long Pegging Awl and the Nutting Girl
Some good traditional songs have been converted by parody into bawdy versions (in the way of Rugby Songs) along the lines of this example which was originally the Black Velvet Band:
This demonstrates another characteristic of some Folk Songs and that is to not-rhyme on purpose, letting an imagined, usually lewd rhyme form in the listeners mind, only to be diverted at the last minute often for comic effect.
Some tunes and songs have been ruined forever by association. The harmless tune and song Redwing had lyrics added about a girl named Nelly Cartwright.