Translation:Is it hot in here, or is that just you?
Ou bien is just an emphatic form of "ou", to highlight the opposition between both options.
I have the same question! If it is being used to address one person, would you ever say this and also use the formal (vous) form of address? That seems wrong. You would be informal, right, and use informal (tu form), right? I still want to know the answer to that question. Can anyone help with that? Separately, I think the vous form would be correct if you were uttering this pickup line while speaking to multiple people. No critique implied on whether that is a bright idea or not. ;-)
This phrase is WRONG WRONG and WRONG. The whole point if it has been destroyed. The correct phrase is.. "Is it hot in here, or is it just ME!" Not "just you" (vous - tu). The meaning is, in its specifically flirtateous context, "Is it really hot in here, or is that MY feeling because you are near." It is NOT an enquiry into why the girl looks like she has a severe case of the sweats... (goodness me!)