"If we were in a physical relationship, you just lost sex tonight". This is a line from the TV show, 'Big Bang Theory'. It seems incorrect but I may be wrong.
Technically, the sentence is not grammatical. The speaker is using the subjunctive mood to express something hypothetical and/or counter-factual (in reality, they are not in a physical relationship). A more grammatically precise rendering would use the subjunctive past imperfect in conjunction with the conditional:
In spoken, colloquial language, the sentence rendered as it was in the TV programme is nonetheless perfectly intelligible, although I'm sure there are lots of self-declared English language authorities who would issue red-faced, frothy-mouthed diktats to the contrary. I will note, however, that as an Englishman this rendering sounds very American to my ear.
Here's a webpage with some nice explanations of the subjunctive mood: https://web.cn.edu/kwheeler/grammar_subjunctive.html
Seems perfectly fine to me.
The first part is expressing a conditional which is not real. We are not in a physical relationship, but if we were, then what follows would be true.
The second part means that the person who is addressed just did something that caused him not to have sex with the speaker. However, he was not going to have sex with the speaker, as the speaker and the addressee are not in a physical relationship.
For the us of this kind of conditional, I believe there is no better reference than the famous song If I were a carpenter:
seems to be a Mixed conditional sentence and is wrong. The correct one should be :
There is a mis-match that is strictly incorrect, but which has rhetorical value.
The first clause is in the subjunctive mode, and so the second part should also be, or at the very least the switch should be less abrupt than it is.
However, consider that the indicative mode of the second clause is much more immediate. "you just lost sex" is much more of a "burn" than "you would have just lost sex".
There's also a further element of humour in this (it is a comedy show after all), in that the speaker has switched from talking about a hypothetical to talking as if it was the case. As well as being part of the increase in immediacy I just mentioned, this also addresses the nature of the relationship in the show, which is (as stated) not sexually intimate, but where it is known that the character addressed wants it to be.
As such, the "incorrect" grammar could be reasonably considered artistic license; not a good idea normally, but used here for effect.