User blog comment:Flagator24/Did Geoff have character derailment in The Ridonculous Race? Theory/@comment-11883116-20170714175203

I'd say flanderization. Geoff always wasn't the brightest one. There was a joke in TDI when a fly flew through his (seemingly) empty head. Even in TDWT, where he seemed to be his most serious self, he still expressed lack of geographical knowledge in Aftermath Aftermayhem, not knowing where Siberia is. His stupidity was taken up to eleven in RR, which means flanderization.

Though I'd say it can be explained in universe. After all, in RR he competes with his best friend, who's even dumber than him, and with whom he likes to goof around.