Similar to the word bullshit but in a sulkier content. It's
something that sucks horrible. Bullshit is used as foul diction for something that is a bunch of nonsense and therefore you can relate bullsuck as its "sister" word, but not as profound. This word takes a lot of pressure built up from that
disappointing moment and allows you to not feel guilty about your language, enabling you to achieve a sense of relief making you feel better
in the end, so it's a win-win situation.