Emma would most definitely laugh at his poor attempt to be serious. Emma doesn't take morons like that seriously. She'd more than likely flip him off after she's done laughing and continue on her way.
If Jack was on PCP, shrooms or drunk when this encounter occurred, probably laugh while approaching and looking at him, thereby freaking out the other guy; or might just curl up into a ball of fear. If Jack was sober, he might figure the other guy is on drugs, and figure that the vision from out of the mask would be severely obstructed, leaving the door open to obtain a new pistol. A pistol that could then be used as a one-off, or traded for a favor.
AI Haley would run him over with several tons of the military vehicle under her control, and be amused at the crunch of bones beneath the wheels.
