1. Frank Castle was once turned black
So, there was a point when comic books could get a little... "preachy" at times. This time, it showed that Punisher's face got really messed up in a fight against Jigsaw (ironic much) and the plastic surgeon decided to make him "black". This was apparently so that Frank Castle could lay low and not be recognizable. The story arc was about Frank Castle having to go through the racial problems that most minorities have to go through on a daily basis in the U.S.A. Within one day of being black, he gets pulled over by the police. Oh and he also teams up with Luke Cage because... He is also a black superhero.
2. The Punisher killed the Marvel Universe
In 1995, Garth Ennis decided to create a one-shot comic book in a sort of "What if" storyline where a bunch of superheroes were accidentally responsible for the death of Frank Castle's family. Frank Castle was distraught to learn that a bunch of people who were sworn to protect to innocent cause him to lose everything. Frank then goes on a killing spree across the Marvel Universe including Spider-Man, Hulk, The Wolverine, Captain America, Daredevil and many more.
The comic book wasn't terribly well received when it first came out 20 years ago but after Garth Ennis got famous after his successful run with Preacher and reviving the Punisher franchise years later, the comic book started getting a cult following. Also, this one-shot comic laid the ground work for the more well-received comic book "Deadpool kill the Marvel Universe".
3. The Punisher once met Archie from Archie Comics
Yep, there was actually a crossover in 1994 that featured the killer vigilante and the cast of Riverdale but would you believe that it's actually not that bad. The crossover follows Punisher as he travels to Riverdale and mistakes Archie has a drug dealer by the name of Red. The misunderstanding is eventually fixed and Punisher eventually teams up with the Riverdale High gang to save the day. While the crossover is initially silly, it's still worth checking out for any die-hard Punisher fan.
4. The Punisher teamed up with rapper, Eminem
Oh yes, Eminem is officially a Marvel character and it is glorious. After finishing up a concert, Eminem get caught up in a fight between Punisher and Bushwacker. Bushwacker soon gets the better of both Punisher and Eminem and tries to kill them on a boat. The comic eventually ends with Eminem saving Punisher's life by chopping Bushwacker to pieces with a chainsaw. You cannot make this sh!t up guys and the only way to truly experience it is to read to for yourself.
5. The Punisher was once turned into a Geisha
In the Marvel's mangaverse, Marvel's badass vigilante went through one of the oddest transformations into a whip-wielding geisha who uses a pendant of "tickle torture" to take down Tokyo crime bosses. By day, she was a normal school principal and by night, she is Tokyo's "kinkiest" superhero by spanking crime bosses into submission. You can't get much more manga-y than this transformation of such a badass and manly character. If you think you can handle this manga comic, then go for it.