Pirates are a nuisance - they blow up your satellites, they harass your universal traders that dunderheadedly fly to that Bliss Place L in the middle of Pirate Central, they break your SETA by their doomed assaults on your ship and, worst of all, they refuse to sell you Plasma Burst Generators. Can I befriend the bastards somehow, so that they stop doing all of that?
Absolutely. The trick, however, is that there are actually multiple pirate factions. Being friends with 1 faction doesn't mean you'll be friendly with another faction.
The easiest way to befriend a pirate is first to have access to a TL so you can do a lot of station building missions. The Elephant is a great choice since its the fastest, but if you got the marines, the Terran Atmospheric Lifter has the biggest capacity and decent speed. Next, spend some time jumping from pirate sector to sector (I like to go to the pirate sector east of PTNI Headquarters as well as Loomankstrat's Legacy. Duke's HQ is another good place to go to, but there's always a M1 or M2 patrolling there so be careful). Fly up to the pirate base/stations there and see if they have any station building missions.
Those are the best at bumping up reputation, and also creates additional pirate stations for you to potentially obtain missions from.
A few things to watch out for:
If Duke's HQ is hostile to you and you think your rep is high enough with them, then what you have to do is force a 'station reset'. Fly into that station and then get the M1 or M2 in that sector to blow up the station for you (by hiding underneath the station), then go away for a period of time until the station comes back, then it should be blue.
If your main goal is to access their PBG forges, then its probably easier to just find a station hacker (they have to be with 2 sectors of the PBG forge) to hack it for you.
The major down side to befriending the pirates is, you'll lose access to those lucrative assassination and defend the station missions. Also, some patrol missions will cause pirates to spawn.