Nicki Minaj's New BF Kenneth Petty Racked Up Prison Violations

Nicki Minaj's new beau is the ultimate bad boy -- and has been for quite some time, including while he was behind bars.

Kenneth Petty's inmate disciplinary history, obtained by TMZ, shows Nicki's BF was written up 18 times from 2006 to 2013 while he was serving time for a manslaughter conviction in New York.

Some of Petty's violations were major -- he got slapped with 2 violent conduct violations in 2010 for threats and fighting. Before that, he also racked up another fighting violation, and 5 violations for disobeying a direct order.

He got off to a ROUGH start too ... just one day after he entered the prison he got tagged for creating a disturbance.

There was also a 2009 incident where he was cited for 9 separate violations, and got 4 months in solitary as punishment. Mostly though ... he lost phone, recreation and commissary privileges for bad behavior.

As you know, Minaj's BF was convicted of first-degree attempted rape in 1995 when he was 16. He served almost 4 years for that ... before the 2006 manslaughter conviction.

Still, the man did his time ... and our Nicki sources say she believes Kenny -- an old flame from Queens -- has changed, and she's happier than she's been in years.