OK, so people from Korea and Japan have been sharing videos of themselves balancing their phones on their boobs/pecs for about a week.
やってみた♥︎ #たわわチャレンジ #1mmでもいいなと思ったらRT
They're doing this because of an anime video that was uploaded to YouTube last week before being taken down for violating the site's community practices. It has since been re-uploaded, but it's still kinda sexual and is based on a lot of illustrations of girls with huge boobs.
月曜日のたわわ その８６ 「ちゃんとこっちも見てくださいね？」 https://t.co/hpZ44A0JtT
After the video went viral, Korean Twitter began emulating one of the characters by balancing their phones and tablets on their chests.
#타와와_챌린지 많은 참여와 도전 기대하겠습니다
Japanese Twitter then took notice and began using the hashtag #tawawachallenge to share videos of themselves balancing their phones on their chest.
やれとの声があったのでやりました これで満足かな？んん？ #たわわチャレンジ #分かりきった結末
"Tawawa" means voluptuous in Japanese, and it is used in this case to describe boobs.
Soon after women began sharing videos, men did too.
#たわわチャレンジ 余裕だった件について まだ見せられる体では到底ないので恥ずかしくなったら消しますw
#たわわチャレンジ 流行ってるからやってみた 肌汚いし白豚ですいません。
こーゆこと？… #たわわチャレンジ
And people got more and more creative.
#たわわチャレンジ こういうことだろ？
이런 시1발 개시1발 #타와와_챌린지
Some people uploaded videos that didn't even have phones in them.
できた #たわわチャレンジ
#たわわチャレンジ 胸に携帯置けるかなぁ〜？ って…落ちた拍子に…*\(^o^)/*