It's in the concentration camp scene at the beginning of the movie, not long after these lines:
Bill: "Why don't we just yuk it up over the school bus crash in the sweet hereafter, Mike."
Mike: "No, no, I'm pretty sure this is a comic book film..."
Then after Mike says: "Now he's going to turn into an X-Person and, uh, he's going to kill all the Nazis, watch, I'm sure that's going to happen!" Bill goes, "Yeah sure Mike, why don't you just pop in [Showa?]
and we can really have some laughs".
I tried searching that phonetically, but didn't have any luck. This stuff goes over my head all the time, Mike and the gang know more about movies than I will ever forget.