This is sad but I completely understand how a constantly barking dog could drive him to this. I’ve personally been driven insane by my neighbors barking dog who barked continuously day and night except when it was sleeping. Pretty much every town/county has an Animal Control Ordinance and all of them have a section on excessive barking which is illegal. Before you grab the gun, try talking to the dogs owners. If that doesn’t work then call Animal Control. In most cases they will have you keep a log for a few days of when the dog is barking. If it’s deemed as excessive they will give the owners a warning citation. A second complaint results in a ticket with (in my county) $500 fine. Yeah the guy was a jerk and what he did was totally wrong. But I do understand his reaction.