I've got another idea, which is 'I don't give a schnit-zel!' This could be quite funny, especially if you pause, after 'schnit!' contracting that syllable a bit so itit's a short sound, and then making 'zel'! a little bit longer than normal.
It will sound like 'shit' and for a moment people might think that, until the second syllable makes them realise that you are referring to a breaded and fried meat 'burger'.