Translation:Is it hot in here, or is that just you?
"Is it hot in here, or is it just me?" is if I were wondering, if the place was actually hot, or if it were just my opinion.
"Is it hot in here, or is it just you?" is, I suppose, a flirtatious remark, implying that the person I am with is hot (the attractive kind of hot hot, not the temperature hot)
It means something in English. I don't know about in German.
In English, it's a play on the phrase "is it hot in here or is it just me?" asking if other people think the air temperature in the area is too warm as the speaker does. The play on words changes "me" to "you" to flirt with someone, implying they are "hot" as in attractive.