Ramen Jigen from Episode 10. Just seeing a ramen-cup kaijin run around was crazy. Also bonus points for the jingle.
To turn it Up to Eleven, there's also the fact that Raita ate that ramen and became crazy impatient that everything, regarding him became plain hilarious, starting from getting him to launch the Jet Machines, telling Ryu to combine... and eventually when Jet Icarus is complete, he had to be tied up to not ruin the control.
Don't forget the fact that right as the sentai are about to pull out their lasers and perform their finisher, the monster just falls down and dies of a previously established Weaksauce Weakness.
Episode 11 as well - the episode with the Vending Machine Jigen. Seeing Ryu being a lazy ass = LOL. Extra LOLs for seeing 'Goody-Two-Shoes' Gai.