。
I'm fed up with his vulgar jokes.
Literal
I [topic-は] his [possessive-の] vulgar [attributive-な] joke [contrastive-には] fed-up-do.
下品 ('vulgar, crude, low-class') is a な-adjective. 冗談 ('joke'). うんざりする ('be fed up with') takes its target with に. The contrastive には emphasizes this specific target — 'especially his vulgar jokes.'