I’ve searched, there were 2 thread that discussed about this but I still could not get the damn thing off…

So, have anyone tried to put a socket on the big end to remove it instead of trying to fit a wrench onto the hex nut?

 

If you remove the spark plugs, you should be able to get an open ended wrench on the fitting nearest the block. It's a bit stubborn, and there's not a whole lot of room to wrench, but I managed.

 

It's not easy to get a wrench on there, I agree it helps to remove other parts nearby. I think I disconnected the spark plug wires from the plugs, I might have completely removed the spark plug wires but that usually needs the throttle body to be removed to access them at the coils. I used an open-ended wrench also. I didn't have the right size socket for the big end of the sensor.