Admit it: You probably laughed at a "That's what she said" joke at some point, but it's getting old now. The setup consists of waiting for someone else to say something that could be interpreted as a double entendre (i.e., "You have a lovely wiener") and then adding "That's what she said" as a punchline, the joke being that "she" sure does enjoy intercourse.
If you've somehow made it through life without hearing this type of joke before, you can find an example in practically every episode of The Office with Steve Carrell in it:
The Old-Timey Version:
"That's what she said" jokes aren't just getting old, they're getting really old. The original version dates back to at least the early part of the 20th century in England, and it came in the form of the way classier "As the actress said to the bishop" -- as in "My dear sir, may I commend you on having an exquisite banger." "As the actress said to the bishop." If you're confused, you have to understand that actors in general were seen as an indecent lot, and the word "actress" was sometimes used as a euphemism for "prostitute," whereas important religious posts have always been known to attract major pervs.
"Oh, I see what you did there."
The first written use of the joke is apparently in the 1928 book Meet the Tiger featuring the Saint (so you can imagine Val Kilmer saying it), but amazingly, it didn't take too long after that for a modified version of the same quip to be recorded on camera, and by none other than a young Alfred Hitchcock.
During a sound test for Hitchcock's Blackmail, one of the earliest British movies to feature sound back in 1929, the director teases an understandably embarrassed actress by saying "Stand in your place, otherwise it will not come out right ... as the girl said to the soldier." Here's the clip:
This was a historic moment in international cinema, with this revolutionary new technology being put in the hands of one of the undisputed masters of the medium for the very first time ... and he chose to use it to harass an actress with the 1920s equivalent of "That's what she said." Considering what we know about how Hitchcock treated his actresses, perhaps this isn't so surprising.
Honestly, we could write an entire article about the history of fart jokes, which are as old as human civilization itself: According to the English study we mentioned before, the oldest surviving joke in the world is a 3,000-year-old Babylonian fart gag. Whoopee cushions, however, are a relatively recent development -- it took nothing short of the industrial revolution and a world war for this clever invention (a rubber bag that makes a farting noise when you sit on it) to appear on the shelves.
Here's an unlikely example of a whoopee cushion in use from an otherwise serious scene in the show Supernatural, of all places:
That's when whoopee cushions work best: When you totally don't expect them. And what could be more unexpected than finding them 1,800 years ago?
The Old-Timey Version:
Apparently the arrival of the modern whoopee cushion was more of a renaissance than a revolution in flatulence humor. As with so many of the great inventions in history, the whoopee cushion has been around since ancient Rome -- and its creator was none other than Elagabalus, the Emperor of the Roman Empire between the years 218 and 222.
Emperor Elagabalus, minus his usual Groucho glasses and exploding cigar.
According to Rome in East by archaeologist Warwick Ball, during Elagabalus' brief and turbulent reign, the emperor did occasionally show a "more likeable side." Specifically, he had a reputation as a practical joker, such as "his practice of seating his more pompous dinner guests on 'whoopee cushions' that let out a farting noise." The prototype novelty item was described as an "air pillow" that would gradually let out the air inside as the guests had dinner, eventually leaving them red-faced and sitting under the table.
So, yeah, for a while the mighty Roman Empire was ruled by a third-century Carrot Top. This makes more sense when you consider that Elagabalus was only 14 when he took over as emperor, and 18 when he was assassinated by his own Praetorian Guard for being an annoying little shit.
For more things way older than us, check out 11 Modern Technologies That Are Way Older Than You Think and 5 Internet Annoyances That Are Way Older Than the Internet.
If you're pressed for time and just looking for a quick fix, then check out The 4 Weirdest Anime DVD Extras (Are Weirder Than You Think).