This question is about "End Times", the twelfth episode of the fourth season.
When Jesse learned that Brock had been poisoned, he came over to Walt's house to confront him. Walt opened the door holding a gun in his hand.
Even though Jesse was obviously mad at Walt, in a couple of minutes Walt left his gun on a couch and walked away, which allowed Jesse to hold Walt at gunpoint using Walt's gun.
Was that intentional?