As nouns the difference between thicko and thicky
is that thicko is (chiefly|british|slang) a dimwit or idiot while thicky is (uk|slang) an idiotic person.
thicko
English
Noun
(en-noun)
(chiefly, British, slang) A dimwit or idiot.
Synonyms
*See also . thicky
English
Noun
(thickies)
(UK, slang) an idiotic person.