My best friend ever on SA-MP up to this day, is definately PiTyFoX, followed be Charlie_Diesel or otherwise known as Charlie_Cortez/[WS]Charlie.
PiTyFox was one of the very few hardcore roleplayers on Argonath. We did many foot patrols, roleplay just hanging out in the PD garage, did vehicle patrols and we were both cadets together. Sadly though, he never made it into the ARPD because we were both to be tested at the same time, and I completed mine, but he didn't get a chance to do his, as the trainer left. He was postponed to take the exam the next day I believe, but for some reason, he never managed to take the exam, and went inactive. So did I after some time.
He was in-game not that long ago, but I havn't seen him anymore. Good thing we're still close friends as I talk to him on MSN. I doubt many of you know PiTyFox, but trust me, he deserves some max respect.
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As for Charlie, I'm sure lots of you know him. He's a great guy, my second best friend ever on Argonath. He's done lots of stuff for me, and he'll always be close. Just hope he gets re-active on Argonath soon enough.