What is the difference between "If I were you.." and "If I was you..." Which is correct?
'If I was you' is grammatically incorrect, unfortunately...
Although 'was' is the normal first-person past tense conjugation of the verb 'to be', it doesn't remain so because we are dealing with a condition: 'if I were you'.
You might want to refer to the Wikipedia article on mood for the full explanation of this: https://en.wikipedia.org/wiki/Grammatical_mood#Subjunctive
Essentially, since this is a hypothetical event with this dependent action going on, we use the subjunctive mood, and the rule for that is... 'If I were you', not 'was'.