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Former NFL running back Brandon Jacobs recently reopened his five-year-old feud with Jim Harbaugh, telling CBS Sports Radio that the former 49ers coach “didn’t know what he was doing.” Harbaugh took the high road in response, advising Jacobs via Twitter to “[l]et all bitterness & wrath & anger & clamor & slander be put away from you, along with all malice.”

Jacobs apparently sought a second opinion.

“I will expose him, Michigan will fire him when I am done,” Jacobs declared Saturday on Twitter regarding Harbaugh.

Before Jacobs convinces himself that he’ll do to Harbaugh what Eric Dickerson did to Jeff Fisher, it’s important to understand more about the history between the two men. Jacobs joined the 49ers in 2012, and a knee injury delayed his regular-season contributions into October. Once October came, however, Jacobs still didn’t do much of anything.

He vented about his lack of game reps, before saying, “I’ve learned over the years when you open your mouth and say certain things, it hurts you, so I’m just going to shut up and keep working.” The next day, Jacobs backtracked, saying he had “ironed it out” with Harbaugh.

Jacobs nevertheless wasn’t activated for the next game, which happened to be against his former team, the Giants. Jacobs finally dressed in Week Seven, against the Seahawks. He nevertheless didn’t play — and wouldn’t play until Week 12 against the Saints.

In November, Jacobs tweeted this general advice: “Never work in a place where you hate your boss so much, you should always be happy at work.” He insisted (perhaps even with a straight face) it had nothing to do with his employment with the 49ers.

Next, he vented again, on Instagram: “I am on this team rotting away so why would I wanna put any pics up of anything that say niners this is by far the worst year I ever had, I’ll tell you like I told plenty others.”

Two days later, Harbaugh declined multiple times to comment on Jacobs during a press conference. Later that same day, the 49ers suspended Jacobs for the final three games of the regular season. He reportedly planned to file a grievance, but there never were any reports of the grievance actually being filed or resolved.

Two days later, Jacobs’ locker had been reassigned and there was no evidence Jacobs had even been employed by the team.

“From the coaching standpoint, they don’t want any distractions on the team. He was being a distraction, they felt he was being a distraction, so they felt they needed to do something about it,” defensive lineman Ray McDonald, who’d go on to create some distractions of his own, said at the time. “I guess, if he’s not about the team. And the coaches feel that he’s not trying to help the team. They made the right decision.”

Jacobs would later say that he was told the team didn’t release him for fear that he’d resurface with an opponent.

So that’s the background, which helps explain Jacobs’ animosity toward Harbaugh. And this isn’t even the first time Jacobs had expressed hostility toward Harbaugh; in early 2014 Jacobs offered up a simple explanation for Harbaugh’s failure to win a championship.

“He is a bitch, and that’s why he’s never won anything,” Jacobs said. “It is what it is. I’ve got two rings. Harbaugh, though, he’s a bitch. So it doesn’t matter.”

It apparently matters now, with Jacobs pointing to the fence and calling his shot: He will expose Harbaugh and get him fired.

That’s fine, Brandon. Now let’s see if you can swing the bat.