At the end of season 3 part 2, we see how Floch Forster isn't pleased with the choice of giving Armin the injection. Lots of poeple talk hate about Floch since then, but actually, I understand his frustration.
Floch was the only surviver of the Beast Titan's attack and found Erwin, dying. He carried a 90kg man to the Shinganshina District, on a roof top. He did all the effort because he wanted to save Erwin.
Floch didn't want Armin dead. He wanted Erwin alive.
Everything he told on the memorial was true, even though it was harsh at times. Levi was being led by the emotions of Eren and Mikasa, who wanted Armin alive, because he was their childhood friend. Levi wanted to give the injection to Erwin, but choose Armin, because of Eren and Mikasa.
Floch thought about the fact that Erwin was the one who could save humanity.
The only mistake Floch made in that scene was the bad timing and the lack of tact. In my opinion, that is the only reason why you may be mad at him.
But also in my opinion, I think people should think twice before they say that Floch was mean. Like I said before, Floch didn't want Armin dead. He wanted Erwin alive. His opinion is not based on emotions, but on ratio. Don't get me wrong, I love Armin so much and I'm happy he's chosen. But when it comes on functionality and if I was there to chose, I would've chosen Erwin.
SnK season 3 part 2 episode 22 (sub); Floch Forster
SnK season 3 part 2 episode 22 (dub): Floch Forster