Worst mistake to ever make in the Pokémon world...

[ShadowXatu]

Mistake Lombre for a human child...(Read its Sapphire Dex entry)
Take a Tyranitar's baby away from it in front of its eyes. Then proceed to taunt it by slapping your butt to it.
Tell an Alakazam it's stupid
Throw a pile of dust on an Altaria. (Apparently it HATES being dirty)
Put an Elekid in an outlet
Let a Cacturne hug you. Poor Cacturne probably never gets hugs
Interrupt a Medicham when it's meditating.
Yank on a Lopunny's ears.
Battle a Tauros with bright red Pokemon.
Call a Hariyama fat.
Try to get in a Kangaskhan's pouch.

[allezlebleus]

In Kanto, don't assume you can't escape Pokémon Mansion, if you don't have escape ropes or dig. I thought I got locked in, in yellow a while back, but I needed to press the switch to get out. I was so angry with my self. I had a lvl 70 Pikachu, lvl 50 Charizard, Venusaur, and Blastoise, a level 45 Muk, and a lvl 45 Pidgeot. I had these lvl's before the 7th gym leader, if only I used my brain back then. Rather than forcing my self into a new game.  =(

[Kdintranet & Scizau]

Not hatching Togepi in G/S/C/SS/HG.

[ShiraBliss]

Leave ur Eevee nad Ditto in the breeders care...

Your Eevee will never forgive you.

never....

[Treecko_addicted? Oh, yes!]

Using your flute on the rancid and uppity old man and giving coffee to the sleeping snorlax.
Don't ask how I know...

[lukey lapras]

forgetting whos in which egg =)

[sylar]

going there in the first place

[Izago]

Getting stuck at Victory Road with a Magikarp no cash no items and no pokeballs. 

I should so try this 

[OranBerrySandvich]

Take Darkrai's iPod and make every track "Barbie Girl."

[Shaymin]

reviving this topic

releasing your starter pokemon

[Specstile]

Eat a cherbu

[Emploneon]

Sitting on a Pokemon Egg waiting for it to hatch. Actually paying Barry when he fines you. Going up against Red in HG SS with LV 40 Pokemon -.-

[Gusparce]

Thinking Kadabra evolves at some high level and not by trading it, so you train it like mad until you find out on the internet when its about level fifty at the third gym. I know from experience.

[Reshurott Inferno]

R+B, on first page, you are 100% WRONG to me. For multiple reasons:
1. I thought you said in your updated squad that you like Blaziken in Gen V was AWSUM because of Speed Boost, which is a Dream World ability, not a 'normal' Ability. So, no SB if you get Torchic as a starter.
2. I like Chimchar, Turtwig, Mudkip, Treecko, Charmander, Squirtle and Totodile better.
3. In Hoenn, Mudkip would be better because it only has 1 weakness, while Torchic would have 4.

[Dracoandy666]

^^ Actually, it's Swampert with only 1 weakness, not Mudkip because it's just a plain Water type.

Finding a Shiny with nothing but your Master Ball left, Or making said Shiny faint accidently >.<

Constantly poking Mewtwo on Facebook.

Calling Shelgon fat and making fun about the fact it can't fly.