Most custom is a phrase that refers to something that is commonly or frequently done or used, or something that is accepted as the norm. The antonyms, or opposites, of the phrase most custom include least common, rarest custom, unconventional, and non-traditional. These terms describe things that are not widely accepted or practiced, or that go against the usual or expected way of doing things. While most custom might be synonymous with tradition, the antonyms suggest innovation, nonconformity, and breaking from the norm. It is important to consider both the most custom and least custom options when making decisions, as each has its advantages and disadvantages.