I figured out how to commit suicide in Croft Manor.

I consistently went out of my way to wreck Jeff Gordan and Dale Earnhardt Jr in Nascar 2005: Chase For The Cup. I also used to get bored, set the laps to maximum and car damage to max (but instantly fixable for the player), turned around and drove the wrong way so I could crash into other cars with the goal of wrecking every driver in the race.

Built a fleet of Terror Stars and extinguished every star* in the galaxy in Galactic Civilizations II.

*Except Sol since you win the game after destroying your last opponent's last solar system.

Not quite absurd, more pointless than anything, but I've spent untold hours driving around in The Getaway 2: Black Monday and Saints Row: The Third (other games too, but mostly those two) with their music muted while listening to whatever album I had just bought.

On a related note, I've spent way too many hours driving around in Grand Theft Auto IIi/Vice City/San Andreas just listening to their in game radio stations. No, I'm not saying that the Grand Theft Auto games have better music exactly, I just mostly played them back when I didn't play on PC and didn't have a Mp3 player.

In Hyrule Warriors I used a power-up Hookshot to pull down the moon from Majora's Mask to kill the dragon from Twilight Princess. That was pretty fucking absurd/awesome.

I've played Deadly Premonition.

Well, in Might and Magic 2, I killed the Cuisinarts without winning any other battles.

I can tell you a few funny things....

In Age Of Empires sometimes a peasant starts whacking another peasant furiously on the ass with his spear when that other peasant gets in the way! damn that looks funny!! And the noise the camels make in that game also cracks me up.... and if you keep clicking on the map quickly to move the camel, it sounds even funnier!

Watching my sisters kid make my elderly mom play unreal Tournament..... i tell you,,, you have not lived until you have seen something like that its that funny..... and poor grandma running along, straight off the cliff into the lava.... bit of a delay in reaction and then "oh dear, what happened?" hahahahahahaha

Lol, I used to intentionally wreck Jeff Gordon too!

Hmmm...Medal of Honor Pacific Assault was one of the few games I owned as a kid, so when I was bored, I would use console commands to spawn tanks, jeeps, artillery pieces, planes, etc, then use the physics weapon (basically force pull/lift/push from Star Wars. It even had an outstretched hand as its appearance) to throw them at enemies. It gave rise to a new definition of "unconventional warfare".

Also, sometimes I like doing as much damage as possible in an RPG.

For example:

Final Fantasy Origins (FF1): I was able to get a monk to do exactly 50976 damage to a frost wolf. (I believe that amount of damage, which is reliable with the right setup, is in fact the maximum possible.) This involves a monk who, without the aid of magic, can do 8000+ damage to most enemies, 6000+ to the final boss (who "only" has 4000 HP), and 3980 to Flans with their insane defense. This is true unless the enemy is hit with a status ailment, in which case some of the monk's attacks miss, leading to lower damage amounts.

Etrian Odyssey 2: I got a Medic to do over 58k damage to a Hedgehog. Further bonuses will cause damage to overflow.

Final Fantasy 5: I was able to get damage overflow to occur here as well. (2-handed + Spellblade (hitting weakness) + level/stat bonuses from bard/mix can cause this to happen.)

Other absurd things I've done:

SaGa 1: I have made most of the bosses die by getting them to run completely out of attacks. (Yes, the game actually keeps track of how many attacks the enemies have left; if the enemy can't attack, it will run away, and if it isn't possible to run from the battle, the enemy will just die.)

Final Fantasy 5: Cast Phoenix without enough MP. When this happens, "Not Enough MP" but the spell's target gets revived anyway. In the GBA version, I was able to get a character to dualcast Phoenix, with the first one appearing to fail completely due to lack of MP, and the second one succeeding. (Undead (from Necromancer) + Dragon's Kiss makes the Phoenix summon have no animation but restore all MP anyway.)

Way back when I first played Genghis Khan 2, the great Khan got married and had his first offspring- in this case a daughter. The game prompts me for a name..being young and immature (unlike now where I'm old and immature) I thought it pretty funny to name my first daughter "Bigtitties".
My advisor then pops up and says "Bigtitties! That's a wonderful name for a daughter!". At 20 years of age I found that hilarious. I should have sacked my advisor though.

Here's another of my favorites:

In Bard's Tale 3, I would send a lone monster out into the wilderness, then D)rop that monster from the party, leaving me with an empty party. Then, when I get into a battle and fail to run away, the first enemy would attack one of my characters (who?), and only then the game would realize that I have no party members and give me a game over.

In Final Fantasy 6, I have managed to get an all dead party, and I know of a way for that to happen in Final Fantasy 5 as well.

It is actually one of the greatest games I've ever played when you get passed the bugs and somewhat weird controls.

I know. It's still weird. :P