I have mentioned this case before, but am re-posting it because I decided to add it to the Case Law Hall of Fame.  It mostly speaks for itself:

Briefly stated, the facts are as follows: In the early morning of December 7, 1960, the night auditor of the Roosevelt Hotel turned, at a noise, and saw a person . . . with a white handkerchief across the lower part of his face and wearing a reddish brown suede jacket, standing a foot and a half away and holding a revolver in his right hand. . . .

Approximately two weeks later appellant was arrested . . . . Later appellant was taken before the United States Commissioner, who explained to him his right not to answer questions, his right to counsel, and his right to ask questions at the hearing.  After the night auditor had testified in chief, appellant proceeded to ask him questions, one of them being the question comprising the first error alleged on his appeal.  The question asked was, "How do you know it was me, when I had a handkerchief over my face?"

At trial, the prosecution offered this as an admission of guilt, and the defendant objected (thus managing the feat of objecting to his own question), but was overruled.  The court of appeals affirmed his conviction.

A dissenting judge said he thought this had been intended as a hypothetical question and so should not have been treated as an inadvertent admission.  Seems to me it was probably both.  It would not have mattered anyway, because four other witnesses also identified appellant as the robber, including one who saw him without the handkerchief over his face because he took it off before even getting out of the lobby.  That mistake seems at least as important as his decision to represent himself.

Nance v. United States, 299 F.2d 122, 123 (D.C. Cir. 1962).