The impatience I encounter is chiefly evidenced by tailgating or by a close dangerous pass when there's oncoming traffic.
I wave back at tailgaters who usually back off. If they don't I take a more dominant road position and make eye contact, before facilitating a safe pass at the next available opportunity.
If I can speak to a close-passer I do so by starting politely - they seem to be expecting an aggressive rant, so a polite & friendly request for more space doesn't usually provoke an angry response. Judging who to speak to, and who to avoid at all costs is something which comes with age & experience I suppose. It's unusual for me to catch up with a close-passer on my routes though.
Ultimately, having cameras front & rear helps me stay calm and gives me reassurance when I do attempt to speak with a driver, as I know I will be able to report any dangerous driving or aggressive behaviour so the Police can decide whether to warn, offer training, issue a penalty notice or prosecute. None of my reports this year have been rejected.