That's not how the math works out, according to Nasdaq.com Tesla's P/E was -53.63 for 2016 and estimated -103.48 for 2017.
And it makes sense: a high P/E ratio indicates high potential. The lower the earnings, the higher the P/E ratio. But if earnings went negative, then the P/E ratio would automatically go negative (since that is how math works, as you say). So if my stock price is $100, and I earn $1, my P/E ratio is 100...so much potential! If I accidentally lost a dollar instead, my P/E ratio automatically becomes -100 even though not much changed in my earnings.