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.