(KJV - Romans 2:1 Therefore thou art inexcusable, O man, whosoever thou art that judgest: for wherein thou judgest another, thou condemnest thyself; for thou that judgest doest the same things.)
Paul spends the majority of chapter one discussing his desire to preach the Gospel and the reasons for that desire. 1) It is the power of God unto salvation, 2) The righteousness of God is revealed in the Gospel; and 3) The necessity of preaching the Gospel is that that the WRATH of God is already revealed from heaven against all ungodliness and the reason for it is revealed. So, Paul desires to preach the Gospel to those against whom the wrath of God is revealed. He ends stating that those against whom God's wrath is revealed understand the judgment if God. Chapter two begins with the statement that because of those facts, we are inexcusable who judges another.
Who am I? Simply one against whom the wrath of God was revealed and to whom the righteousness of God was revealed through the preaching of the Gospel. What evidence is there against me that I judge people. The obvious are those times that I judge someone's thoughts or intents of their hearts. All I can see are the actions, but the thoughts and intents are hidden from me unless they reveal them. Why would God tie the revealing of His righteousness through the preaching of the Gospel to judgment? My failure to give someone the Gospel is because I judge them unworthy of hearing them, and therefore worthy of the wrath of God. Why else would I hold the truth in unrighteousness? Fear? Of what? The persons reaction. I have judged them as one who would reject the Gospel.