I don't have a huge dick (it is above normal size though) and I like to incorporate the following routine:
Walk up to a girl "Hey thanks..."
Her "For what?"
Me "For giving me a boner" (Only had one girl dislike this, also this is the easiest way to start a conversation about your dick)
Walk up to a girl "Hey thanks..."
Her "For what?"
Me "For giving me a boner" (Only had one girl dislike this, also this is the easiest way to start a conversation about your dick)