suck at--

--が苦手・---が下手

"That sucks!" = 「最悪！」とか「もういやだ！」という意味もあります

1. I really suck at giving speeches.

2.

A: Did you hear? We're not getting our bonuses this year.
B: No way! Really?! Man, that really sucks!

3. What?!! You forgot to bring my money again?!! You suck man!!