Is there a safe way to loosen an O2 sensor? I’ve tried a wrench and a ratchet. Any suggestions? Can I use WD40 or another lube?
I hope you’re not trying to remove this thing with the exhaust system cold. A cold exhaust pipe contracts and makes the sensor harder to remove. Enough effort would probably rip away the threads.
The exhaust should be hot (or at least very warm), so that the metal expands and makes sensor removal easier. Virtually all sensor threads come coated with anti-seize compound to make removal easier, but first drive the car around and get everything warmed up. Wear some thick gloves because the exhaust and the sensor will be HOT.
I don’t recommend using any sort of spray lubricant as that’s a fire hazard. Shouldn’t go spraying that stuff on a hot exhaust pipe. 
I warmed it up. I have the burn marks to prove it. It still won’t budge. Any other suggestions?