Ad Muminem, where you attack someone's mum instead of answering the question/argument. Here is an example:

Quote Originally Posted by Person A
"When philosophy discovers something wrong with science, sometimes science has to be changed — Russell's paradox comes to mind, as does Berkeley's attack on the actual infinitesimal — but more often it is philosophy that has to be changed. I do not think that the difficulties that philosophy finds with classical mathematics today are genuine difficulties; and I think that the philosophical interpretations of mathematics that we are being offered on every hand are wrong, and that 'philosophical interpretation' is just what mathematics doesn't need."
Quote Originally Posted by Person B
"well um your mum is what mathematicians don't need"
Make up your own logical fallacies, now!