Taking Vega with me on all missions has given me the opportunity to see most of his nicknames for the crew.
Shep is Loco/Lola,
Garrus is Scars.
Tali is Sparks.
Cortez is Esteban.
Javik is Buggy.
Liara is Doc.
I haven't seen him refer to Ashley, Kaidan, or *spoiler non DLC squaddie* by a nickname. I don't have Ashley in this game, though. I think he may have called her Ash like everyone else does in my other game.
Javik and Liara cracked me up. And you'd likely only see him use the nicknames if you brought them together on certain missions.
And yeah, I liked him before, but using him in every mission has had him grow on me. Easily one of the best human squadmates.
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Gamertag/PSN-Murphiroth
"Would have liked to run tests on the seashells..."