For example when he criticized Megyn Kelly as having "blood coming out of her wherever" implying that she asked him a tough question because she was having her period.

http://www.cnn.com/2015/08/08/politics/donald-trump-cnn-megy...

And here is a long list of examples compiled by the Telegraph: http://www.telegraph.co.uk/women/politics/donald-trump-sexis...