The Entire Jethro Tull Album "Thick As A Brick" is a parody of several Progressive Rock
concept albums, but to a degree specifically of the Who's "Tommy".
The fact that it simply wasn't recognized as parody by any of the album's
intended targets makes the joke funnier. Yet as a work standing by itself
"in a vacuum" it is regarded by serious Tull fans as a masterpiece.
Now as for simple direct laughing so hard that I literally piss myself Weird Al Yankovic has never accomplished that... Bob Rivers did several parodies that did... even on the tenth listen I go to the bathroom before pressing "play"
His best are:
Heart's "Dog & Butterfly" became "Doing it Doggy Style"
AC/DC's "Dirty Deeds Done Dirt Cheap" becomes "Dirty Deeds Done With Sheep"
KISS's "Rock And Roll All Night" becomes "I Used to Rock And Roll All Night"
And finally a Version of "Stairway To Heaven" as it would have been if the Beatles
had recorded it. Though Dred Zeppelin's cover of that some (done to a Regae beat
with an Elvis impersonator singing! ) sticks with me a lot more (hearing stairway after
hearing that version twice will still make you laugh yourself to asphyxia)
IF you've never heard of Beatallica and you like either the Beatles or Metallica look
them up on the web (most tracks are free legal downloads)
One other excellent parody I've never identified as to the original artist is a parody of the
B-52's "Love Shack" converted into a side splitting parody called "Love Shaft"