I just watched Justin from "Playing Board Games" in his Gauntlet Challenge with limited card pool facing this guy, and a question arouse, which neither he, nor people in chat could answer (correctly). So since I lost my password to comment on youTube, and can't recover it either, and more so, I feel, if a guy, who professionally plays Arkham all days and clearly knows more about the game than me, is uncertain about a thing, chances are, there are others, who didn't watch the video, yet would like an answer, I decided to answer it here.
The question was, if Brown would force to discard The Tower • XVI, if his Forced ability triggers, and the answer, they came up with was: "No, because only randomly discarded weaknesses can leave the hand", but that's not, what the rules say.
The relevant paragraph of the rules is: A player may not optionally choose to discard a weakness card from hand, unless a card explicitly specifies otherwise. So while cases, where a card is discarded randomly, like with Liquid Courage or some treacheries, are probably the most common and hence often used as example, they are not the only time, this can happen. The Forced ability on Brown Jenkin does not leave an optional choice, it simply gets rid of your whole hand, no matter what. (Unless you are Patrice, having the Watcher from Another Dimension in hand, because that is a hidden card, which cannot leave your hand by any means except those described on the card, so it trumps the general rules for weaknesses.)
I also think, this is intentionally. Both the weakness and the enemy came in the same cycle, the former can even be "earned" as a story asset, and they didn't went the way to fix it, neither in the errata, nor optionally in the "Return to". And it would have been an easy fix, if they wanted that. Just replace the text with: "Each investigator at his location discards each non-weakness card from their hand..."
There are other weird edge cases, I want to highlight, even though, they are unrelated to Brown Jenkin. It's fairly obvious, that if you draw Amnesia, while holding a weakness in hand, you have to "choose" all other cards. But what happens, lets say, if Winifred draws Amnesia while holding The Tower • XVI and Arrogance in her hand? My take would be, that in this case, she would have to keep both weaknesses, because she cannot choose, which one to get rid off, so she has to keep both, doing only as much as possible from Amnesia's revelation effect. But people might make a case, that that's where the otherwise redundant "optionally" from optionally choose to discard kicks in, saying that, there is no option to keep two cards with Amnesia. I'm not sure on that, but would go with my interpretation unless proven wrong. Even if you also hold a hidden card plus a weakness, Amnesia does not allow to choose even the weakness, you are obliged to do as much of Amnesia as possible, keeping both cards.