Fock E Oh

What does it mean? More importantly, what does it sound like? Lets say it slowly:
F o c k E Oh.
To me, it sounds like a 2 year old saying Fuck You. We aren't sure. Twice we have disciplined Will tonight by telling him sternly not to do something. We get Fock E Oh shot back at us. We try hard not to laugh. I have to convince myself that's not what he's saying. It can't be. Could it? Oh boy.