What does Proverbs 23:2 mean?

This verse uses the technique of "hyperbole:" exaggeration for effect (Matthew 5:30). Just as people in modern English might say, "I've told you a million times," those phrases are understood to be poetic, not literal. In this case, Solomon is advising a student about the need for self-control when one is hosted by a ruler or other powerful person. Rather than give in to greed and overeat, he should be polite. That's important enough that, symbolically, it's better to put the knife to one's own throat, rather than to the food, if that's what it takes to not appear greedy.

In context, Solomon is speaking about the impression one gives to a host, especially someone in a position of authority. The general idea also extends to greed and gluttony, in general. Gluttony is one of many sins which stem from the cravings of our fallen human nature. Like all other lusts, gluttony must be put aside. Paul writes, "Let not sin therefore reign in your mortal body, to make you obey its passions" (Romans 6:12). Fortunately, the believer does not have to give in to the passions of the sin nature. Paul explains in verses 3 and 4 that believers are united with Christ in His death and resurrection and therefore can "walk in newness of life." In Romans 8:4 believers are described as those "who walk not according to the flesh [the sin nature] but according to the Spirit." Knowing how the sin nature fulfills its evil desires through the deeds of the body, Paul practiced a strict discipline. He writes in 1 Corinthians 9:27: "But I discipline my body and keep it under control, lest after preaching to others I myself should be disqualified."