His first reaction is arguably his best. The first monster he sent to go clear up Godzilla was the heavily despised American "Zilla", who is the said monster from the 1998 Roland Emmerich film. X has an anger meltdown after seeing Godzilla use his atomic blue breath to wipe out Zilla after a 13-second fight, but then he immediately comments he knew "Tunahead" wasn't up too much, which is Toho Studios shouting Take That! at Roland Emmerich.
Another is after the Gotengo crew has been captured and brought onboard his ship. He's mid-breakdown when they come in and goes "Just a sec," finishes, then turns around to confront them.
Godzilla fighting Rodan, King Caesar, and Anguirus. After Rodan is down for the count, Anguirus rolls into a ball and does a combination attack with King Caesar, which is basically KC kicking Anguirus like a soccer ball, with Godzilla playing goalkeeper. Seriously, Godzilla jumped to catch the Anguirus-ball like a goalie! And MISSED! Right after that, King Caesar makes an expression that either says, "Man! I missed?!", or, "Dude! How could you miss that?!".
Just the fact how long it takes Godzilla to defeat his American counterpart. To put it bluntly: 13 seconds.