5. You killed roughly 9,999 people at the end of Portal

portal

You might not know it, but the classic FPS/puzzle title Portal actually had two endings. There was the happy ending, where Chell escapes her imprisonment of the Aperture Science Facility with the help of a gigantic explosion. But when the sequel was gaining steam, this was later retconned into the "Oh crap, we need to get her back inside for the sequel" ending which was stapled onto the game via a patch. 

It was a necessary move, since Portal 2 opens with the protagonist, Chell, waking up from an unspecified time in cryogenic sleep. The A.I. known as Wheatley tells Chell that the ten thousand people in the other test chambers are now dead due to the reserve power running out.

portal wheatley

What both Chell and the player are probably blissfully unaware of is the fact that you were responsible for these deaths at the end of the previous game.

The details of your monstrousness were explored in yet another officially licensed comic. Portal 2: Lab Rat was like the Tomb Raider books in that it functioned as connective tissue between the prequel and sequel. It mostly follows one Doug Rattmann -- also known as the guy who was leaving all of those creepy notes on the walls in the original Portal -- in his attempts to save the unconscious Chell at the end of Portal 1. Rattmann has a hell of a time of it though, since the Extended Relaxation Center (aka the cryo-chambers) were actually destroyed by Chell when she finished off GLaDOS at the end of the first game.

portal comic

The loss of GLaDOS meant that the power to the ten thousand stasis rooms has gone offline, meaning all of the people inside have died. That's why everything looks abandoned/derelict/Detroit-y at the beginning of Portal 2. The only reason Chell survives is because Rattmann spends the comic re-routing the remaining emergency power to her Relaxation Unit. 

But that's only half of your KFC Double Fuckup Sandwich. By defeating GLaDOS at the end of Portal, Chell also destroyed the only person who could fight the Combine. As in, the bad guys from the Half-Life games. This is something that GLaDOS is more than happy to tell you in-game.

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Having a super-computer with access to reality-distorting portals could have been really handy in stopping the invasion, but nooo, Chell just haaad to leave Aperture Science. Hell, if Chell had her way, she'd probably have already ran face-first into a headcrab by now. 

Neither Portal 3 or Half Life 3 look like they will be coming out anytime soon, so you can at least pretend Chell died of old age. Which is also likely what will happen to you before Valve stops selling Dota hats and makes another game.