In his appearance in the fourth Pokémon movie review, which wasn't released until after his death, he leaves the review early, angry and depressed.
There's an entire episode of YCPT where JewWario slips and has a near-death experience in the bathroom, which is absolutely cringe-worthy and nigh-unwatchable now if you know the circumstances around his death.
In Suburban Knights, Todd in the Shadows threatens to shoot Justin with his (fake) gun. Justin took his life via gun.
His Monster Rancher retrospective about his time with the Japanese version (known as Monster Farm), especially when he says toward the end that he'll slate his beloved Golem into Monster Farm 2 "maybe someday."
Nightmare Fuel: For such a light-hearted show, Negadub is quite creepy and malevolent.
The way he kills JDub is pretty disturbing, too: as Justin comes down the stairs, the Negadub steps out in front of him with an eerily serene grin on his face; Justin glances down...and sees a knife sticking out of his gut.