The stupidity of youth? . Generally each generation of youth atempts to reinvent their language thinking they are the first to do so and innovative. It's a natural thing to happen. . "Sucks" has become such a widely-used term that it is a negative, but extremely generic in meaning. . I suspect that "sucks" has become a category or an adjective. That's red. That's good. That's (of the category called) sucks. . Whatever the pseudo-justification, I think the important points are; (1) The general meaning is sort of obvious, as with most very generic things. (2) It's not something you;d want to be heard using, unless all those you hang out with use the same expression and you have a real need to be seens as one of them. Just my view. See what other views you get. Someone who says this sort of thing, might be able to give you more detail on the justification that in their mind makes it a great things to say. :) Enjoy.

Hahaha, I won’t use ‘that’s sucky’ myself!! But it’s really good to know these stuff. Thank you again Tom!

You're welcome, Keiko. "Sucky" is one of those words you probably shouldn't use it as it's not technically correct. However, it's helpful to recognize it when you hear it :) As is probably the case in all languages, native English speakers tend to take a bit of "poetic license" and invent words for various reasons (e.g., emphasis, being cool, etc.). An example of that is "ask". "Ask" is a verb, but it's become commonplace in American culture to state "What's the ask?" as thought it were a noun. You obviously speak English very well and as you become more and more fluent, you'll, no doubt, run into this quite a bit.

Thank you Tom! ‘Sucky’ was new to me! And make sense because it looks adjective.

It would be "that sucks" or "that's sucky". The latter isn't technically a word ("sucky"), but is used colloquially.