'Real Housewives' Brit Lisa Vanderpump DISSES Prince Harry -- He's Got a Tinky Winky!

Prince Harry's package is so small ... he shouldn't be allowed to call himself a prince at all -- this according to British "Real Housewives of Beverly Hills" star Lisa Vanderpump.

Lisa was out in Beverly Hills earlier today when we asked if she's seen the pictures -- and she must have been living under a rock the last 12 hours ... because she hadn't.

So our camera guy showed them to her on his phone -- and Lisa replied, "I need a magnifying glass to see that! Hold on, let me get my glasses."

Once she got a good look, Lisa handed the phone back in disbelief, saying, "That's not a ROYAL penis!"