To quietly and calmly lose one's mind, stab someone fifty times, slice bits of them off, consume those bits, decapitate victim, then display the head as a trophy to shocked bystanders. See postal.
Darren is at the end of his rope with the Japanese account. I'm worried he might go greyhound on them.
To go crazy and stab the shit out of people. Like "going postal" with a knife. Also, Greyhound's advertising slogan.
Dude had a knife and decided to Go Greyhound on people. The police tased the shit out of him.