There are millions of licenses out there, so that is not possible to say. But if you pick one of the standard ones (that not contain any curse words), you should be good to go.
I presume you’re referring to the WTFPL, Jeff Atwood’s preferred license. Ironic, isn’t it, given we’re using Discourse? On a more serious note though, WTFPL has some practical aspects worth looking into if you’re able to look past the specific language. Please consider spending some time reading up if you can.
Based on my experience it’s unacceptable to promote a theme component in the Hugo forums if the component is licensed under WTFPL, even if the license isn’t mentioned in the promotion (awareness) announcement.