In Iron Man 2, Stark created additional Iron Man suits. During his birthday party, however, Rhodes was able to take and put on one.
In a later dialogue, Nat said this shouldn't be possible. To quote from the movie scene (the one where they where in a donut shop with Nick Fury):
Nick: Is that even possible?
Nat: Well, according to Mr. Stark's database security guidelines, there are redundancies to prevent unauthorized usage.
Tony, however, didn't answer the question.
So, how then was Rhodes able to steal and use it? Did I miss something from the movie? I could not recall him ever wanting to take on a partner or sidekick, nor did he express any signs of wanting to have one.