I don't really like converting people to One Piece, since, to be honest, I think that to some, One Piece just really isn't their type of show, instead preferring to watch shows like Naruto, Elfen Lied, Hellsing, etc. Not attempting to bash on any of those shows, really; just mentioning what I've seen a friend of mine enjoy watching more than OP, lol. O_o
Seriously, though, I used to be fanatical on this, making attempts to try and convert that same friend of mine to watch OP as soon as possible, because after just having gotten hooked to it, I genuinely couldn't believe that he wouldn't like it if he just gave it a shot. :P So I literally found him online on Playlist.com one day and literally typed in, "DUDE, YOU HAVE TO WATCH ONE PIECE!! IT'S JUST THE MOST AMAZING SHOW I'VE EVER SEEN!" like a crazy bastard, but was unsuccessful. :P
Eventually, after consistently and consistently bombarding him with requests to watch One Piece he came over to my house, and we hung out for a little bit, and I decided to show him a little bit of One Piece (episode 405 to be exact), only to be dismayed when he made bitter, negative comments on it that made me grimace, eventually erasing the impact and emotion the episode initially had on me and forever burdening me with those unforgettable words (which I shall not tell :P). The reason this had happened, though, was because during that day, he was currently infatuated with Death Note, and was also trying to convert me into a DN fan. O_o So when I began showing him OP episodes, he wasn't interested at all and was focused solely on making me like Death Note, while I was trying to get him to like One Piece. Yeahh…my regrets are many...:P
But, anyways, aside from my rants of self-pity, I guess what I'm basically trying to say is that, two primary factors on "converting" someone to One Piece, is
[[B]A]: The way you introduce it to him/her; aka his/her first impression.
[[B]B]: How this person sees One Piece's fans. (For example, say this person is on Youtube, watching an AMV of Fullmetal Alchemist, one of their favorite, most precious shows. Then he/she sees a comment that says, "Fullmetal Alchemist f***ing sucks! One Piece is way better!" This person will instantly have a peculiar disliking to One Piece, whether he/she knows it or not, because [Well, in my opinion, at least. :P] a lot of people tend to judge things based on what they think of the individuals that like it, which is why I also mention that…)
But yeah, that's all I really have to say, and my hands are getting really tired, so I think I'll just turn off my brain processes for a second and just give some last, direct "advice" towards the main question of this thread, lol.
Episode 19's nice. 384, 474; they aren't half-bad either, though. In my opinion, if your friend thinks One Piece looks goofy and quite kiddish, (that's not entirely false, though, by the way), show him Movie 6, at the least. The nice animation and darker theme might give him a stronger nudge to the rest of the series itself. ;)
So yeah, other than that, that's all I got, lol. This is one year late, but whatever…:P
Hope you get your friend going, and have a Merry Christmas. O_o