My vote: when Marge and Homer are hiding in the barn loft and the farmer says something like “If anyone’s in here, they’re in for some serious ass-forkin’!”
I’d say Kent Brockman’s exclaimation about New Springfield being so rich they take ‘golden showers’ comes close.
I think that it is a toss up, either the time when Marge entered the demolition derby and was being repeatedly smashed into by another car and Homer yelled “Stop banging my wife” or the time a woman was on the sea captains boat and Smithers said "I do’nt think women and seamen should ever be together " to which Mr Burns replied “we know what you think.”.
“Sneed’s Feed and Seed (formally Chuck’s).”
formerly even
Principal Skinner tells the hamster(gerbil?) to “chew through his ball sack”.
And in the same episode, Groundskeeper Willie says, “You won’t have your willie to beat around anymore” (or something to that effect)
Mmm… sugar walls.
“Now, whenever someone gets wood, they’ll think of Trojans”
I can’t think of the episode, but Homer is listing great inventions and ends with…“and the glory hole.”
Springfield Heights Institute of Technology
4 words:
“Gentlemen, start your whacking.”
Homer pinched his ‘Candy de Milo’ off the babysitters butt - & is in a world of sexual harassment trouble – an Inside Edition type show interviews him and splice’s the interview:
“I grabbed her sweet sweet can (splice) her sweet can mmmm (splice) …”
it goes on like that quite a while.
Wasn’t there another episode where a captain commented on Marge being aboard by saying “women and seamen don’t mix?”
I think the “Golden Showers” line takes the cake, but here are two others that might warrant a mention:
Sea Captain (to Apu): Thank ye for these copies of Juggs. They’ll keep me men from resortin’ te homosexuality - fer about ten minutes. [Sailors laugh, and one quietly chides “Look who’s talking.”]
Bart: Oh, come on, everybody knows the first day of school is a total wank.
Skinner: If by wank, you mean ‘educational fun’, then let’s get wanking!
That was Marge on the boat: it was the Halloween ep with King Homer Kong.
I don’t get the Chuck’s Feed and Seed one.
I think the Golden showers one is pretty good.
There was also the whole “Now I’m Dick Tracy! Now I’m Pruuune Face” thing with kid Ned.
Feed and Seed rhyme with Sneed. This of two words that rhyme with Chuck and start with F and S. I’m not sure this was the intended joke, but it’s funny.
Oh man, I forgot about that one - I almost died laughing when I got it (not the first time around). What little Neddy says, while destroying building blocks and stuff, is “I’m Dick Tracy. Take that, Prune Face! Now I’m Prune Face. Take that, Dick Tracy! Now I’m Prune Tracy. Take that-” VERY abrupt cutoff. 
It’s time to get Homer erotic
These are all good ones!
I also like the one where Marge is commisioned to paint a picture of Mr.Burns and when it’s shown Mr.Burns comes to Marge and say’s “thanks for not making fun of my genetalia”, when she paints him in the buff!
I just saw a rerun of the “Marge gets sugar banned” episode, where the judge calls the sugar magnate a “hershey highwayman.”
I don’t remember the exact episode, but when Homer says that he likes his “homosexuals flaming” I remember being very surprised.
[sub]hee hee “Flaming Mo”[/sub]