How to talk about theory
You may be working with rude elitists, but from my experience, being reluctant to explain technical details depends more on the context than on the person I am talking to. I would usually avoid giving technical details of a proof/algorithm over lunch or in the corridor even if my interlocutor were Alan Turing himself. The reason is that details heavily depend on the choice of notations and on hand-crafted concepts introduced to smooth a claim. Also, because everyone understands things differently and I do not have a generic way to explain a concept, I always have to adapt to my interlocutor (that is why giving technical details in a research presentation is so hard by the way).

One exception is if my interlocutor has worked closely with me on this kind of problem and then, I know that we can use this common gibberish that only we understand because we grow into it together after several white board sessions (or before an urgent deadline).

Another exception is if after giving a crude overall scheme of the proof without details, my interlocutor asks a precise question showing he has seen a particular hard part of the proof that I have been intentionally hiding from him in order to simplify the presentation. In that case, we would naturally open the Pandora box and go together into the heart of the proof, layer by layer... and usually end up on a white board because at some point, we again need this common gibberish that only fit us and this problem.

There are several morals with my already too long story:


Do not depreciate yourself because you are not actively working in theoretical computer science. Most people will not care about your precise background as long as you show that you are curious about their work.
When people are vague about a proof/concept, stay alert and try to guide the conversation by asking a precise question showing your understanding and thus helping your interlocutor to choose which part of the proof he should develop first. This is obviously quite hard and unpredictable because you may not be able to give relevant comments on the go (this happens to everyone even to "theorists"), but if you manage it, then you will likely end up with a very enlightening discussion.
Even "theorists" need time to reload the details of a proof in their head before being able to clearly explain it. Make an appointment by explicitly asking that you are interested in the technical details of X. This will allow for time for your interlocutor and you to prepare, and will ease the discussion. Make sure to have a white board or a piece of paper during the discussion so that you can really go into details.