He's saying that even if there are things he still needs to learn in his job, he knows how to wear the good looking uniform with style. When you have something down ("have it down pat") it means you have mastered how to do it.
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Grammar GeekThx! I think I got the idea now..:-).
....Be patient, you won't learn it all at once - celebrate your successes so far, like looking good in the cool pants.