The "Beecham's Pills" parody of "Hark, the Herald Angels Sing" comes with a story. It seems that the local laxative manufacturer offered to provide free hymnbooks to the church, if it would be allowed in insert one advertisement. That seemed fair, and indeed, it appeared that the company had left out the advertisement. But next Christmas, the parishioners found themselves singing....

The version I heard (St Andrews University, 1958) ended

How can man to art aspire
If is soul is not on fire?
How can man crawl into bed
With his belly full of lead?

The version of the Twelve Days of Christmas current at the same time & place had

12 twisted twats
11 lecherous lesbians
10 torn-off testes
9 gnawed-off nipples
8 aching arseholes
7 sex-starved spinsters
6 convicted vicars
5 choir boys
4 Boy Scouts
3 dirty whores
2 shithouse doors
and my Lord Montague of Beaulieu

-- the last having been had up for sodomy in a then fairly recent scandal.

The following, IIRC, is by E. Gorey:

Hark, the herald angels sing:
Glory to the newborn Thing,
Who, because of radiation,
Will be cared for by the nation.

Also in a somewhat filkish mood, I believe I saw the following in a fanzine some years ago:

It came upon a midnight clear
And ate up everything in sight.

Finally, from Caltech ca. 1962 I recall

O Christmas tree, O Christmas tree,
Oh, piss on thee, O Christmas tree!