Impugn (verb): Dispute the truth, validity, or honesty of (a statement or motive); call into question.
Source: oxforddictionaries.com
In the essay Michael Ian Black mentions “I got dozens of messages impugning my manhood; the mildest of them called me a “soy boy””. Here he means that people began to question his manliness. So they mock him by calling him “soy boy”. I understand he is trying to convey the doubt he received from the people who mock his masculinity.
Diana Galvez