The Tuk Tuk dudes in Siem Reap are just brutal, although I wouldnt call them aggressive or intimidating.
My method is when they say "Hellooooo Papa", I merely respond: "No need Weed, no Ketamine, no morphine, no lady boom boom, no ladyboy" and they usually laugh and hunt someone else down.
I don't get that in Bangkok at all, in any tourist area. Africans yes, Indian watch sellers yes, Taxi guys, no. Not in front of any hotel, not in front of Thermae, no where. They may quote a stupid price but a smile and no thanks and they go away.
Maybe the OP brings it on himself by going full yob on some poor Thai guy who asks if he wants a ride. We will probably see a post from him entitled "Gang of Taxi dudes beats me up". Can probably understand why.