sex organs or
So the literal meaning of
脏话 stands for some words about sex organs used to insult people, that is to say,
这里能说脏话吗？ stands for
May I speak F-words here?
Also, another example mentioned by user fabregaszy:
我能说脏话吗？不能？那我就没什么可说的。 stands for
May I speak F-words? No? Then I have nothing to say. It shows that the speaker is extremely angry of this decision so I have to say nothing except F-words to the decision maker.