"Why Bottoms/Bums/Sphincters/Poo and Farts are Funny"

Firstly we must establish whether buttocks and their offspring are indeed funny at all.
Fact; there are a lot of jokes about bums and bum holes.
Fact; sometimes people laugh at these jokes.
Fact; Life contains an seemingly endless series of harrowing disappointments, bitter underwhelming anticlimaxes, ‘hallmark’ shallow sentiment, all too transparent cunning, avarice and stupidity only punctuated rarely with brief quiet moments of mere tedium…But I digress.

The sphincter is rarely funny in and of itself. Its merely the muscular end of a tube that our species has evolved to transport fecal substances hither and thither. Our function is and has always been, to process organic matter while moving about collecting and depositing it, in effect being dumb vehicles for sophisticated nutrients.

What this produces however is without question the first comic asset available to each and every one of us. We produce shit…We hunger and we produce excrement.
It belongs to us… we made it ourselves. Its strange, smelly, dark, textured stuff that we have no real need to keep or hoard or sell off or trade.

When we first discover it as small children we may experiment with painting or target practice or make-up but shortly after the first freelance attempts at improvisation (look mum… a beard just like dads!) we learn that the one thing we know we can do, regularly and without fail… Is not to be dwelt on, or discussed or focused on for recreational purposes.
The whole defecation dimension, the whole shit strata, the whole psychological cacophony of ka-ka is repressed, flushed from polite society, cast aside to lie rejected yet reoccurring, quietly percolating comedy....
Repression breeds tension and tension is the bedrock of comedy.
The release of tension via laughter being the comic science.
Comedy 101 being the framing of tension and expectation and providing tangental and well times gates for release.
However theory aside…

Bums are naughty (titter titter) , Poo is unmentionable (giggle giggle)
Farts are unseemly ( Clutches sides, trembles, collapses)

While children universally find emissions of gasses and semisolids endlessly amusing , the hilarity generally wanes in the female subspecies at about 5 or 6, while for males to one extent or another it seems to be a permanent condition.
I think that, even in the vaguest sense, realising that, as a female you can produce offspring, generally overshadows other, less socially acceptable objects the human body produces, that could be dressed up and pushed around in prams.
Boys like the humour inherent in shit because they identify with its seemingly pointless nature.
Girls on the other hand,having a regenerative ace in their back pockets (either subconsciously or otherwise) are better equipped to handle social stuff in general and less prone to explode into hysterics at the introduction of the turd concept.

The idea of sticking objects into and up the bottom is funny in part because it applies itself to every insecure heterosexual males worst nightmare (and there is only one secure heterosexual male in existence and he lives on a mountain in Tibet with his head buried in lava ingesting yaks yogurt via osmosis and incredible muscle control as he sits on a tub of it and slowly sucks it up backwards through his body.)
Just as its an ironclad comic principle that a grandmother in an out of control wheelchair heading for a cliff is always funny unless she’s your grandmother,
so too is the idea of arbitrary objects penetrating bums funny as long as its not your lower bowel.
( I am not addressing the not insignificant minority who do this very thing gleefully and as sport or sexual sacrament regularly)
I would suggest that the tension exists for females as well simply because their bottoms get invaded more often in the real world than anyone else's. (as a kind of anal fashion statement on the part of their partners more than anything else and on their part an occasion piece of variety,… like wasabi.)

Shit in small part and farts in larger part (because they have a largest public marketshare-it being rarer to shit inadvertently) is funny as a reminder of mortality, a group of people being suddenly subject to the stench of decomposing matter have little choice but to deflate the tension via laughter.

Farts are also funny because they are aural, they speak…they have different tones and its interesting to note that however long they may be people always wait until the end before laughing, farts are rarely interrupted but they certainly bully their own way into situations which brings into question their status.

Farts can be used as weapons of mischief, as comic timing devices used to socially punctuate situations, they can be used to deflate importance in others, they can be used as a form of heckle.
Inadvertently they can also be comically humiliating (see granny and the cliff)Buttocks are funny because they have mystery, (your own that is)

Buttocks are one of the least observed parts of your own body, they are obviously tangible (else your legs would never meet) but they exist socially almost as much as they do literally. They advertise lots of subliminal pelvic thrust info.
(They are the equivalent of offal thrown into the sea to attract sharks. )

The mathematics of an ideal woman's waists/hips/ buttock width has actually been rendered as a formula of attraction that has remained constant throughout recent history using quantified leering males and old masters as subjects. Is this funny?

Well only if you can see the humour in being a knee-jerk automation existing only to reproduce and die while deluding yourself that your personality, your occupation, your relationships are anything other than cunning deceit’s designed biologically over epochs to make your life appear worth living just until such time as you’ve bumped into someone, become overcome with hormones masquerading as emotion or thought and either spilt seed or incubated.
I’m not veering off topic, rather asserting that for all its cerebral finesse, for all the ways we convince ourselves of our sophistication in humour and other topics. The 2 year old looking in amazement at the shit in the palm of his hand and chortling later in life as a ripe blast punctuates the classroom threatening the teacher with loss of authority, thats really who we all are and all we all have.
And thats funny.