Name commomly used by the gaming community to describe a noob or someone that generally fails at everything. The name was created when a Call of Duty 4 and Runescape player with the name "X Timbob X" (or TimmyD94) famously admitted over his computer that earlier that day he had had sick, perverse thoughts about his mother naked. Thus, his name was turned into a general insult and is now used worldwide, and when mentioned will always create an uproar of laughter.
How did you miss that shot? Dude, he was like a meter away from you, you're such an XTimbobX!