Initial thought is that an armed man, confronting another openly armed man, to talk about how he is wrong, could end badly.
However, upon further review, I might consider the following, if my family were not present.
Strike up a conversation, play dumb, invite him to sit for a cup of coffee. Let him talk, pontificate, bloviate at length, and then after careful evaluation, possibly reveal that you too are enthusiastic about the 2A. Share what you do to increase awareness and further the shooting Sports.