I think he might have been talking to the priest we see at the end, though not everything he was saying at the beginning fits that view.

I think of DeNiro's Johnny Boy as his second best performance, after LaMotta in"Raging Bull." Keitel was wonderful, too. "Mean Streets" has that almost-magical Scorsese talent for making scripted scenes look like they're ad-libbed. The scene in the back of Tony's bar when Charlie is haranguing Johnny Boy about paying his debts, and they're talking about the girls "Is she the one on my left, or your left" will never be surpassed.