First was that idiot Spencer who made himself an obvious target straight away by approaching Negan with designs on Alexandria's leadership. Spencer evidently considers himself something of a worldly diplomat in the mould of his late mother, former state governor and head of Alexandria before the arrival of Rick Grimes. Turns out he's just a kiss-ass and a wimp. Negan, never one to pass up an opportunity to make a point, saw through Spencer's schmoozing immediately -- and made that clear in a big, messy way. After cutting the poor guy down as a gutless coward in front of the entire Alexandrian populace, the bruiser proceeded to slice him in more literal ways, resulting in a very dead Spencer and a whole lot of grisly innards on public display. That's Negan for you: he'll spare Carl despite attempts to kill him because he admires the gall and audacity. But sneak around and try to charm the guy? That's when you get a knife to the belly.
Spencer wasn't the only one who failed to survive the hour. Olivia, the friendly matriarch figure whom Negan already threatened twice (with death and sex both), took a bullet to the face after Rosita took aim and shot at Negan, missing him but leaving her homemade cartridge lodged squarely in the side of Negan's bat Lucille. Instead of retaliating, Negan punished Rosita for the act by determining who made the bullet in the first place. Negan appreciates the nerve of the thing: he actually seems to like Rosita, attempt on his life and all.
We know well that it was Eugene who manufactured the ammo on his own in an abandoned factory near the town, and after a bit more pressure -- Aaron's little-seen partner nearly lost his life too -- Negan discovers this little fact for himself. That's useful information and even more useful talent. So naturally, Eugene, once revealed for all his skills, got himself kidnapped and whisked away to the Sanctuary. Who knows what fate awaits the poor guy. Probably a bad one.