This answer is 100% SFW.
Current !$^%@ Resources
Although my groups (and I) generally don't swear, this is a tool for conveying meaning. As far as I am aware, there is no official selection of such words for goblin or orcish. This fandom site has some words, it lacks those really good, grandmother-offending swear words.
Swearing depends on the culture! However, a surprising number of swear words revolve around religion, body parts, and reproduction.
Additionally, a number of languages treat comparisons with animals as swear words. For instance, calling someone a pig in English is insulting, but not enough for fisticuffs. Calling a German a pig, however, gives them a good reason to punch you in the face. A similar thing goes with calling someone a dog in Middle Eastern cultures: it is a severe insult! (Thanks @KorvinStarmast)
Swearing in %$^&ing Fantasy
Your best method is to devise your own phrases, maybe only using the direct translations. If you and your group are like most people, you are likely translating most words into a language your group understands, so just translate or substitute equivalent words.
If you are not like most people, and you are developing orcish/goblin into an actual language, you will need to make your own swear words. Once again, using religion, body parts, and reproduction should give you a solid starting point to get something really offensive.