Question

Everyone from that department is untrustworthy.” This is an example of (the post-hoc fallacy. the red-herring fallacy. the group-think fallacy. the hasty-generalization fallacy.

Answer 1

If you were to say that everyone from that department is untrustworthy, you would commit a hasty-generalization fallacy. This fallacy would be comprised of the fact that you're making a final judgement based on a few datapoints you have about certain people.  

Answer 2

"Everyone from that department is untrustworthy.” From the sentence, you are judging directly without any examples or enough evidences. Using few examples and making conclusion then and there to represent the whole, then you are making a "hasty-generalization fallacy."