I'd be like, "OH SH*T!!!" And then punch it multiple times and then once it doesn't know what's going on I'll run out of my room and if it follows me I shall throw thing at it and lead outside to let it get run over by a car >:)
step one yell or simply say wtf.
step two punch several times to distract it.
step three when distracted run to kitchen and grab my favorite knife.
step four stab it in the back and hope it wasn't prank.