Como eu digo "nu em pelo" em inglês

Português: nu em pelo, totalmente pelado, do jeito que veio ao mundo.
Inglês: in the buff, (as) naked as a jaybird, as naked as the day someone was born.

Exemplo 1: 'I'm more naked than the women!': Daniel Craig jokes he is in the buff 'most of the way through' No Time To Die and says Bond shouldn't be played by an actress as they 'deserve their own roles'. Ref. dailymail.co

Exemplo 2: "We get him up, and he's naked as a jaybird, " Hayward Police Lieutenant Gary Branson said. Ref. manchestereveningnews.co

Exemplo 3: Almost as noble as James Broughton's willingness to stand there as naked as a jaybird is his willingness to use babytalk. Ref. independent.co

Exemplo 4: (...) we might object if somebody wandered into that gallery or Underground station as naked as the day they were born. Ref. portsmouth.co

Cf. Como dizer "Ficar pelado, Ficar nu" em inglês