Agent Hotchner: This is Special Agent Dr. Reid.
Man: You look too young to have gone to medical school.
Agent Reid: They are PhD's. Three of them.
Man: What, are you a genius or something?
Agent Reid: I don't believe that intelligence can be accurately quantified, but I do have an IQ of 187, an eidetic memory, can read 20,000 words per minute...yes, I'm a genius.
Reid: Can one of you do me a favor?
Morgan: Sure kid, anything you want.
Reid: Can one of you at least look like you're going to see me alive again?
[Hotch has just been strangled.]
Gideon: Take your tie off for once in your life.
Answer: "The Boogeyman", s02e06. Spoiler alert: The kid is Jeffrey Charles and at that point he had already killed 3 other kids. Jefferey basically hated and resented other kids after his mother abandoned him and his father spent a lot of time with other children because of his job. Jeffery would lure kids Into the Woods and then beat them to death with his bat just because of hate, no particular "reason." The scene you're describing, Jefferey agrees to walk Tracy home when her "buddy" leaves her (at this point the FBI announced there's a serial killer on the loose and kids should walk with a buddy). Jeffrey gets mad at Tracy for walking too slow and for complaining, and he takes a swing at her, causing her to flee Into the Woods and have Jeffery chase her.
Bishop73