With the boggart now focusing it's attention on Harry, the almost trance-like state Ron had been in broke.
"Just ignore it, Harry," he offered helpfully. "It's not real." As if he'd forgotten that just a minute ago he was reaching for his wand to destroy Bellatrix.
"You're dead," he informed Voldemort.
The boggart turned to him, and though the sight was imposing, Ron didn't have the same experience with the Dark Lord that Harry had.
"You forget so soon, do you? That it was I who killed your best friend?"
"He's standing right there," Ron retorted. "Maybe we could just ignore it?" he suggested to Harry.