Instructions
Finding Mr. Lopez
Head to Rivet City. It is a city made out of an abandoned aircraft carrier in the southeast corner of the map. You must travel through the ruins of Washington, D.C., to get to it, which can be very dangerous with all the super mutants running around, so bring lots of ammo and health packs (stimpaks).
Go through the Rivet City Marketplace, which is the first door you will encounter when you enter the city, and keep following the signs on the walls until you reach the Flight Deck.
Wait until between 8 a.m. and 12 p.m. in the game or between 3 p.m. and 5 p.m. in the game to find Mr. Lopez, a grisly old man, standing over the observation deck.
Talking with Lopez
Go up to Mr. Lopez and point the cursor at him, then press the "A" on the Xbox 360, "X" on the PlayStation 3, or left-click on the PC to begin a conversation with him. This will give you several conversation options.
Convince him that he is pathetic by selecting the negative conversation options. After which, he will jump off the observation deck, leading you to gain negative karma, which is the game's way of keeping track of how well you have behaved, and will adjust in-game content accordingly (some players will refuse to interact with you if you have negative karma).
Convince him to help out Ted Strayer by clicking the option with the "[Speech]" next to it. If your speechcraft skill in the game is high enough, Mr. Lopez will decide not to kill himself and to instead mentor the Rivet City resident Ted Strayer. This option will give you positive karma.