Scream crying aaahhhh!!!

I dont think this is a case for toughening up as much as teaching him how to deal with a plethora of emotions that include anger, confusion, uncertainty, anxiety and disappointment. All children react differently to facing these difficulties and dilemmas. Some, as your son, resort to screaming and tantrums, some become reticent and withdrawn and others may be overly confident or appear arrogant. All of these are natural responses. First you need to acknowledge that his screaming ishis reaction to something he feels is significant whether or not it is over something you feel is 'nothing'. What he needs to learn is how to appropriately respond to different things in different ways. An effective way of doing this is by demonstrating for him a wide range of options to use yourself when the situations arise. So when you stub a toe let him sees you are cross and upset. When you drop something insignificant a simple oops would suffice. Use vocabulary in response to something upsetting that he could mimic and that is developmentally appropriate. When he does appear to 'over-react' respond by telling him and showing him a response more appropriate than screaming. Dont react to his upset by shouting or screaming yourself. He will only feel confused by your upset. Given time, good role models and an extended vocabulary he will hopefully learn a whole range of more appropriate responses.