I personally think this is just an expression this character uses but it isn't actually grammatically correct. I think it's just a funny expression which doesn't make sense grammatically. I wouldn't worry about it too much! Hope this helps

It depends what he's talking about. If he's talking about a group of people, you would really expect to see/ hear an 's'. On the other hand if he's talking about a situation and a number of contributing factors to that situation, this could explain why he doesn't use an 's'. I haven't heard this expression used in this way before, but maybe he has just adapted it to the context. It could work like this....

"I understand that "a bunch" of anything is always plural." Well theoretically yes but you can sometimes twist language to your own purposes: For example if you we're in a really difficult situation with many problems coming on top of each other, I can imagine somebody saying: "What a bunch of s**t!" Similarly, you can sometimes use nouns as adjectives in an innovative way; so it could be possible to say something like: "The situation is just weirdo...", even though it is not the conventional use of this word...

Oh, ok so "weirdo" in this case is uncountable then. Like "shit." It doesn't mean "a weird person". It means "weird shit". I think I get it now if I understand this correctly.

I agree with the points Charlie made, but personally I've never heard anyone say anything like this, and I would have assumed it was a subtitle error if you hadn't said otherwise. Normally, "weirdo" is a singular, countable noun, just as you thought. It CAN be used as an adjective ("this is totally weirdo"), but using "weirdo" as an adjective is not normal -- it SOUNDS weird (and kind of funny). Using it as a non-count noun seems completely strange to me. I don't know the context of the show you're watching, but I feel like the speaker may be using weird grammar as a (somewhat comical) way of verbally reflecting the weirdness of the person/situation he's talking about.