Bobby Simmons once told a federal grand jury all about the night he was robbed at gunpoint in 2006 by a member of Chicago’s so-called “super gang,” prosecutors say.

But when the one-time NBA player took the witness stand Thursday in front of six alleged leaders of the ultraviolent Hobos street gang on trial for racketeering, Simmons forgot all about it.

“It’s kinda hard,” Simmons, wearing a gray sweat suit and muttering softly into a microphone, told Assistant U.S. Attorney Timothy Storino. “I can’t remember everything that happened. It was so long ago.”

In the end, Simmons’ memory loss cost him another day in court. Defense attorneys wanted to take the weekend to consider what to do with him, and the judge told Simmons to come back Monday. Patrick Blegen, attorney for Paris “Poleroski” Poe, called Simmons’ testimony “terrible for the defense” — because Simmons seemed scared.

U.S. District Judge John J. Tharp warned Simmons he would be held in contempt of court if he doesn’t return Monday. Prosecutors said it took a significant effort by the FBI to serve Simmons with a subpoena.

Simmons waited more than an hour to leave the Dirksen Federal Courthouse in an effort to avoid news cameras. When he finally walked out the door, he broke into a sprint and giggled as he ran away on South Dearborn.

Simmons was a member of the Milwaukee Bucks at the time of the robbery. The feds say Poe stole a $200,000 white gold and diamond necklace from Simmons outside a North Side night club. During a car chase that followed, the feds say Poe opened fire on the former Simeon High School and DePaul University forward.

The seemingly memorable night was apparently very forgettable to Simmons, once he was under oath.

Simmons told jurors he didn’t remember how much he paid for the necklace.

He couldn’t remember what kind of car he leapt into to chase the men after the robbery.

He didn’t remember his grand jury testimony about what happened.

And at one point, he said he didn’t even remember testifying before a grand jury.

Finally, Tharp called a sidebar to speak to the attorneys in the courtroom about Simmons’ testimony. Poe, who had been watching Simmons’ testimony from a defense table, took a sip of water and leaned back in his chair.

Simmons has previously been reluctant to testify against the Hobos. The gang has been described as a “conglomerate” and “an all-star team of the worst of the worst” of Chicago’s street gangs. Its members have been tied to nine murders.

Poe allegedly executed two informants who snitched on the Hobos to the Chicago Police Department and the FBI.

But in June 2006, the feds say Simmons and several others chased Poe after Poe stole Simmons’ necklace. Poe fled in a car driven by alleged Hobo Arnold “Armstrong” Council and allegedly shot at Simmons’ car. Poe eventually jumped out of Council’s car and ran before Council crashed, according to prosecutors.

Simmons held Council at the scene of the crash until police arrived, the feds say. Later, they said Simmons became nervous about identifying Poe and Council to authorities because he “heard word on the streets that both Poe and Council were extremely dangerous.” Simmons feared for his life, they said.

Simmons also received “mysterious phone calls” from people asking him about the case, according to court records. It wasn’t until Poe and Council were arrested on separate charges that Simmons agreed to cooperate against them, prosecutors say. Poe and Council pleaded guilty to Simmons’ robbery in December 2010, records show.

Prosecutors say Simmons never got his necklace back. And Council wound up suing him.