Tsukkomi Gesture

In Japan, a backhand slap on someone's chest, or, sometimes, doing the gesture on air, suggests the person is doing a tsukkomi ツッコミ, a "retort" calling out something stupid that someone else said, which is typically done in manzai 漫才, a type of comedy routine with a duo of comedians, namely the boke ボケ saying stupid things, and the tsukkomi calling out the boke.

Aioi Yuuko 相生祐子 doing a tsukkomi on Minakami Mai 水上麻衣 by slapping on her chest with the back of her hand.

Left: Minakami Mai 水上麻衣
Right: Aioi Yuuko 相生祐子
Anime: Nichijou 日常 (Episode 1)

Examples

For reference, some examples.

Manga: Mairimashita! Iruma-kun 魔入りました！入間くん (Chapter 54, 正反対の入間)

Context: Suzuki Iruma 鈴木入間 makes Valac Clara ウァラク・クララ sit on his lap in class. The entire class stares at them. In response, Iruma says:
nanda yo
なんだよ
What is [it]?
[What are you looking at]?
mise-mon janee zo
見せもんじゃねーぞ
[This] isn't a show.
- mise-mon - contraction of mise-mono 見せ物, a "thing," mono, that you "show," miseru, others.
pii
ぴー
*head smoke noises*
Hearing this, Andro M. Jazz アンドロ・ジャズ retorts, making a gesture slapping the air:
iya, {dou mitemo} mise-mon daro
いや　どうみても見せもんだろ
No, {no matter how you look at [it]} [it] is a show.
- iya - "no" in the sense of "no, what you said is wrong:" this is clearly a show, and you're obviously doing it in front of everybody for everybody to see it.