2 Peter 3:16 "There are some things in them that are hard to
understand, which the ignorant and unstable twist to their own
destruction, as they do the other Scriptures."
This verse is occasionally used by individuals following the 'Hebrew Roots' movement (among others) to discredit New Testament Theologies based heavily on the letters of Paul. Hermeneutically though, since Peter's text here relates to Paul's letters, this question really should be asking which Pauline letters Peter is referencing - though unfortunately, most answers to such a question are inevitably opinion-based.
This sort of verse could theoretically be used to discredit virtually anything an individual sought to disagree with from Paul's letters. But we don't have enough information from this text to make any links with any particular Pauline texts - the text is too vague to render any solid hermeneutical case as to particular applications.