The episode "Grandma's Kisses" contains some adult jokes.
Patrick tells SpongeBob that in order to be an adult he has to say "Tax Exemption" and acquire a taste for free form jazz.
Grandma gives SpongeBob an "adult" book titled "The Technical Manual for Routine Maintenance".

big meaty claws-fish guy
Well these claws are just not for attracting mates- Mr Krabs

When Plankton gets out of jail and he tells Karen come on baby you know I just got out of stir
End of line

Sponge Bob out of water, the nuts Sandy Cheeks fills her mouth with come from Mr. Nutter.
http://imgur.com/gallery/w3iuA

Spongebob making a balloon Squidward out of condoms.
When the regime of Dragons fell, the reign of Stags took over.

When Plankton switches lives with Mr Krabs - in the beginning when he is about to be shot out of the ketchup, he puts on a mask that looks like a gimp/bondage mask rather than a helmet.

The episode,
Dumped
. Gary starts spending more time with Patrick, and Spongebob gets upset and tries to make Gary jealous, then eventually begs him to come back.
When Patrick comes over with Gary to do laundry, he takes off his pants, and Gary goes into them to get a cookie. He eats it, then belches, and goes right back to Spongebob, leaving Patrick in tears in his underwear screaming "I thought what we had was special!"
So, Gary just wanted Patrick's cookies, not him. And now that he got his, he's goin back to Spongebob.

There was the one fish insulting Mr. Krabs' instrument playing, saying he had big meaty claws. Mr. krabs then says the claws "ain't for just attractin' mates!"

Karen 2.0
Plankton is getting tired of Karen, so he builds another, who has a slick hourglass figure. Karen calls her cheap. Plankton throws out Karen classic, and she cries that Plankton dumped her for a "newer model." Karen also calls her a homewrecker and a hussy.

I couldn't exactly remember how this one went, so I looked up the transcript. In "Komputer Overload", Plankton become estranged from Karen and makes a risque joke about being solo-
"Oh, curse you cruel fate! Once again, you've left me covered in the sticky goo of my own folly. Only this time, I'm all alone."

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Just saw this episode this morning :
When The Flying Dutchman is staying at Spongebob's house and throws a wild party Spongebob walks in on Dutchman hitting on one of the guests, that might not be all that adult oriented until she asks "Is that a wedding ring?" At which point The Flying Dutchman throws the ring away and it lands on Spongebob's nose.
I thought, "Did they just do an adultery joke?"

"Karate Choppers", where Spongebob and Sandy can't stop thinking about doing karate. Some pretty heavy sexual subtext
Thought I was the only one who got the sexual connotations.
You dodge a question like a character dodges a punch on Mortal Kombat.-IceJJFish

"Karate Choppers", where Spongebob and Sandy can't stop thinking about doing karate. Some pretty heavy sexual subtext
My redneck cousin pointed this one out to me, in the episode with the Alaskan Bull Worm, there's a scene with a realistic Sandy vs a worm that looks just like a penis.

explain.

"It only seemed to increase their appetite for wieners!"

The don't drop em joke.

don't forget also in d and d: the part where they're in a guillotine and Spongebob is about to die; gets his head chopped off.