Here's one where the sexual meanings are a little more obvious. Of course, this doesn't prove that the bawdy versions are any older than the non-bawdy versions. From Bodleian Library Broadside Ballads, Harding B 11(47), no date given.

Anybody know what "firing" means in verse 3?

THE RIGS
And Sprees of this Town, or
POP GOES
The Weasel.

Come all you lads and lasses gay, and listen with attention,
And of the sprees of —— town, I presently will mention.
With Jack & Will & Tom & Bill, and Bet with Mary Teasel,
I took a move into —— town, and there I popt the Weasel.

And now I've got into —— town. Believe me what I say, sir.
With the pretty girls in this place, I'll have some gallant play, sir.
I can dance and sing and merry be, & play with Mary Teasel,
And when we get into the dark, pop will go the Weasel.

There's tradesmen here of every kind and some that are fond of firing,
And the pretty girls in this town, I'm sure they are admiring.
And when the dance it does begin, they'll come with Master Teasel,
And before they go home at night, I'm sure they'll pop the Weasel.

Now you can pop the Weasel, Bet, and so can Nell and Kate then,
But in nine months, my darling girls, how sad will be your fate then!
You'll curse the day that you did play along with Roger Teasel,
Or on the grass you tumbled down & learnt to pop the Weasel.

Now Nelly she does rue the day, and so does Mary Anne, sirs.
Look at the size; you may easy tell the thing that I do mean, sir.
The other night in going home along with Farmer Teasel,
We had not got far from the town before pop went the Weasel.

You may talk about the jolly lads that come to —— town, sirs;
They are the lads I do declare to do the thing that brown, sirs.
They can walk out and take the arm of young Miss Lady Teasel,
And before they do return again, they play Pop goes the Weasel.

Now pop the weasel, Bet and Jack. Pop it in and out then.
Pop the Weasel, Joe and Bet. Don't let them pull it out then.
When going home, now don't you stop along with Master Teasel,
Or you will rue the day you learnt to dance Pop goes the Weasel.

I'll end my song—it is not long—but tell you in a trice, sirs:
I'd have you all both great and small just take some good advice, sirs.
When homeward bound, don't tumble down along with Master Teasel,
Or he will spoil your muslin gown when dancing Pop goes the Weasel.