すっぽんぽんutterly stark naked, wearing only one's birthday suit

お風呂(ふろ)に入(はい)るためにすっぽんぽんになる。

To take a bath, one becomes utterly stark naked. {utterly stark naked, wearing only one's birthday suit}

子供(こども)達(たち)がすっぽんぽんで水遊(みずあそ)びをしています。

The children are playing in the water utterly stark naked. {utterly stark naked, wearing only one's birthday suit}

すっぽんぽんの時(とき)、人(ひと)は一番(いちばん)無防備(むぼうび)であると言(い)える。

One could say that when a person is utterly stark naked, they are at their most vulnerable. {utterly stark naked, wearing only one's birthday suit}

大(だい)浴場(よくじょう)には、すっぽんぽんの人(ひと)やタオルを一(いち)枚(まい)纏(まと)った人(ひと)しかいない。

In the large bathhouse, there are only people who are utterly stark naked or wearing only a single towel. {utterly stark naked, wearing only one's birthday suit}

鏡(かがみ)ですっぽんぽんの丸裸(まるはだか)の自分(じぶん)を見(み)るに至(いた)って、太(ふと)ったことに気(き)づいた。

Upon seeing myself utterly stark naked in the mirror, I realized that I had gained weight. {utterly stark naked, wearing only one's birthday suit}