One of my personal nightmares is to see 4chan-tier memes and insults find their way into the original Japanese script. Instead of being something localisers insert themselves.
Unfortunately, that day may legitimately happen before I die; Toshiaki-kun (Japanese Anon) is aware of 4chan and studies them to figure out what the heck is wrong with their brains. Part of this is due to Nishimura Hiroyuki being a household name among Japanese kids, so Hiroyuki owning 4chan is like him owning a zoo filled with weird and exotic creatures that say outlandish nonsense. But because of this morbid fascination, Gigachad has become a loanword in Japanese, so the title of this thread is incorrect. The word exists in Japanese, and we're all the worse for it.
Chad: チャド
Gigachad: 男性性の塊のような男、ギガチャド
Gigacock: 雷のような男性器、ギガコック
Chad Gigacock: イケメンで筋肉質、チャド・ギガコック
座ワルド & ギガチャド
座ワルド & ギガチャド
Basically, expect to see a Chad cameo in a manga or anime in the near future.