I am hot.

Yes, you can say it. It has more than one meaning.

You could avoid confusion by saying, 'It's really hot today, neh?' Just don't say, 'It's getting hot in here', I mean, unless you want to hook up.

I would not think of the "****" meaning except in a situation that was already flirtatious* or already directing me towards those thoughts. If a random person said to me that they were "hot" I would think only of temperature.

(*Not that I can remember situations like that very clearly now!)

PeterTJust don't say, 'It's getting hot in here', I mean, unless you want to hook up.

Can't somebody say that if they are referring to the weather or the temperature, say, inside a room or a building? If I, with my friends, am sitting in a room and I say "It's getting hot in here", won't they understand that I'm talking about the temperature inside the room?

Yes. Context makes such matters very clear.