Without knowing your friend or your backgrounds in music it's really difficult to say what is the best entry as there's so many.
Generally I think for anyone who wants someone to get into it I think it's important they develop an ear for it, and many of us I'm sure came up the same way.
Some variation of:
Throbbing Gristle, Coil, Nurse With Wound etc, while simultaneously hearing stuff like Merzbow but not having a developed enough ear to not have our brain just overwhelmed and miss the pattern recognition until finally it clicked. Probably hearing Wolf Eyes, Dilloway and a lot of that era of American Noise...
If your coming from a metal background I think Sunn, Ride for Revenge, rawer black metal, moving towards noise rock. Then I remember stuff like Nicole 12 being pretty listenable, there's better "more musical" Power Electronics releases and honestly it's been so long since I've listened to any of it I can't say what those are. I remember some Grunt being like that, obviously late period whitehouse.
I think a person getting into noise does a lot of personal listening work because they want to understand it, and if a person lacks that they probably won't get into it. But in my experience with friends that were at least open to me playing weird music when we hung out they had the best experiences in understanding it by seeing it performed live or fucking around and making Freeform sound together which made them a more active participant.
My list of potential stuff I might tell someone to check would be
Robert Turman
Dilloway and Turman Blizzard (I like the cassette best, but the collab cd is what I am talking about), then Dilloways stuff like Concealed, the Squid with C. Spencer Yeh.
If they like grind, Sissy Spacek then other Wiese
Emil Beaulieau Americas Greatest living noise artist (think it's on YouTube)
Smegma nattering nayboobs, and then you could use that as a jumping off point to the Plays by Smegma/Merzbow album helicopter putout.
The main thing is to avoid creating some impossible listening barrier by just overwhelming their ears, I think people find there way into the more harsh stuff in time.
One of the first releases I bought was a swampland tapes the Rita, and let me tell you, it was not a good entry. I kept returning to it intrigued but it never did and that project has never done anything for me.