Determining who the "worst" custom motorcycle builder is would be highly subjective and dependent on individual preferences and opinions. The custom motorcycle industry is diverse, with many builders offering unique styles and approaches. Some builders may be more skilled or experienced than others, but it's important to remember that artistic expression and taste can vary widely. What one person may consider the worst, another might appreciate. It's best to approach this topic with an open mind and explore different builders and their works to find what resonates with you personally.