Test Eng, a Vermont Teddy would be nice...except they discontinued the one with a straitjacket!
Misery does love company... no profit letting this sad sack make you miserable too!
Otherwise, it is also true that you catch more flies with honey than vinegar... all you can do is keep the 'welcome mat' out, and hope they either come around, or find a new target for their angst.
Rather than dwell on this loser... use him as an intro to your many fine neighbors. Them concetrate on them, and your happy experiences.
If there's one thing a loser can't stand, is the sight of others ignoring him, and having fun!