expression, noun
extremely bad at; dread; really dislike
Emphatic phrase for something one is very poor at or strongly averse to. Often used with ～が大の苦手 or ～は大の苦手.
私は人前で話すのが大の苦手です。
I'm really bad at speaking in front of people.
彼は早起きが大の苦手だ。
He really dislikes getting up early.
大嫌い expresses strong hatred, while 大の苦手 focuses more on inability or strong aversion rather than pure hatred.
Combination of 大の (great, big) and 苦手 (weak point, dislike). The exact historical derivation is uncertain, but it functions as an emphatic set phrase.