A number of the What Ifs are hilarious due to the completely insane, but perfectly logical, conclusions (and, sometimes, the sheer insanity of what is being logically considered in the first place). Others are hilarious for the irrelevant but amusing tangents the author sometimes goes off on.
* [[http://what-if.xkcd.com/1/ Relativistic Baseball]]. A question about pitching [[spoiler: nukes a city]].
** of course, in that case, the question wasn't exactly straightforward. Still, the conclusion, in context, is arguably one of the funniest things on the site; [[spoiler: A careful reading of official Major League Baseball Rule 6.08(b) suggests that in this situation, the batter would be considered "hit by pitch", and would be eligible to advance to first base.]]
* [[http://what-if.xkcd.com/4/ A Mole of Moles]]. No insane ending, but it nevertheless involves [[spoiler: a moon-sized ball of meat and fur that periodically erupts in plumes of boiling guts]].
* [[http://what-if.xkcd.com/6/ Glass Half Empty]]. The standard optimist-or-pessimist question [[spoiler: leaves people with shards of broken glass embedded in their faces]].
** "Free glass!"
* [[http://what-if.xkcd.com/8/ Everybody Jump]]. A rather simple question of kinematics becomes [[spoiler:a Class 1 Planetary ApocalypseHow.]]
* [[http://what-if.xkcd.com/10/ Cassini]]. A detailed and thoughtful exploration of climatic interactions concludes with [[spoiler: ''Radio/APrairieHomeCompanion'' being attacked by fire ants and alligators]].
* [[http://what-if.xkcd.com/12/ Raindrop]] features some absolutely brilliant bits of wordplay, one in each of the last two paragraphs:
--> Fear reigns supreme as the world fears rain supreme.
--> ...and the unexplained meteorological phenomenon is simply dubbed a “Skrillex Storm”—because, in the words of one researcher, “It had one hell of a drop.”
* [[http://what-if.xkcd.com/13/ Laser Pointer]]. A question on light ends with [[spoiler: the moon becoming a rocket engine and Earth suffering a Class 4 Planetary ApocalypseHow.]]
* [[http://what-if.xkcd.com/19/ Tie Vote]]. A question about elections ends with this gem, with an image to match:
-->...when one of the Florida electors reaches into the hat to draw a name, [[spoiler:he or she is struck by a falling cocaine bale, the hat is hurled away within the next few seconds by a tornado, and the elector is obliterated minutes later by a meteorite impact.]]
* [[http://what-if.xkcd.com/21/ "Machine Gun Jetpack":]]
---> ''(Stick figure has attached a rear-facing [[GatlingGood GAU-8 Avenger]] to the top of a car.)''
--> '''Cop:''' Do you know why I pulled you over?\\
'''AltText:''' actually, what i'm confused about is 'how'.
* [[http://what-if.xkcd.com/24/ Model Rockets]]'s punchline is a CallBack to [[http://xkcd.com/1133/ Up Goer Five]].
* [[http://what-if.xkcd.com/42/ Longest Sunset]] kicks off the article by defining what qualifies as a sunset and what doesn't. Examples of the latter include the sun crossing the horizon partway and then reversing direction, the sun ''splitting in two'' and half of it setting, the sun ''landing on the horizon and hatching like an egg'' (AltText: "you bred sun-raptors?"), and a ''square sun'' that doesn't get a chance to do anything before the narration cuts it off (AltText: "aww, man, you didn't even let me try").
* [[http://what-if.xkcd.com/43/ Train Loop]] discusses jet-engine-powered trains.
-->Sadly, they never took off. Fortunately, they never took off.
** "Ok, putting the jet engine on top didn't work. Maybe we should try something different." So he puts the jet engine on the bottom, so the train can't make contact with the tracks and tips over.
-->...why did we think that would work? Forget that idea.