As adjectives the difference between gloppiest and ploppiest
is that gloppiest is (gloppy) while ploppiest is (ploppy).
gloppiest
English
Adjective
(head)
(gloppy) gloppy
English
Adjective
(er)
soft and soggy; mushy. ploppiest
English
Adjective
(head)
(ploppy) ploppy
English
Adjective
(er)
Making a plopping sound.
(British, puerile) Relating to excrement.