A way of saying "one thicc boi". The "un" is the masculine indefinite article, meaning "a", from the Spanish language. "Thicc boi" is from the English language, and when combining these two phrases, makes a Spanglish sentence. This is a better way to say "one thicc boi" and is, from experience, more likely to get laughs. Sometimes you can say "un hella thicc boi" but that can be a bit over the top.
(Eighth graders learning about U.S. History)
Person 1: (whispers) Washington was un thicc boi, am I right?
Person 2: (Trying to muffle their laughter) Hell yeah!!!
Person 1: (whispers) Washington was un thicc boi, am I right?
Person 2: (Trying to muffle their laughter) Hell yeah!!!
by rootbeer&icecream May 4, 2018
Get the un thicc boimug. 
by TheRealKamori July 6, 2019
Get the Thicc hundredmug. by T H I C C C Cness June 11, 2018
Get the Thiccmug. by protestucatto November 16, 2019
Get the thiccmug.