VERY helpful video and photos - thanks!
What you are describing in your 6 year old Boxer-Boston (Boxton? Boster?) appears to be Pyoderma.
Pyoderma is a bacterial skin infection that is seen as red pimple-like lesions or red circles usually found in the groin area, and the armpit area. The little red spots may look like tiny pimples and they are filled with bacteria and pus.
Let me explain a little bit about how this can happen...
There are normally small numbers of bacteria living on the skin surface, but when they invade the skin like this it is called pyoderma. This can happen if there is a small scratch, flea or mosquito bite, or cut in the skin surface. It is particularly common when the weather is hot and humid, as the bacterial and yeast numbers are very high in those conditions.
Pyoderma causes the dog to be very itchy. Think of yourself if you have a small scratch on your arm - it may become very itchy if it gets infected. Then multiply that by 100 and you can imagine how itchy your poor dog may be!
If this rash is in more than one small area your dog will need to go on oral antibiotics to get it under control. Oral antibiotics for skin infections are often given for 2-4 weeks in order to resolve the problem. Often, when dogs are as itchy as Rocky appears to be, I also put them on a course of anti-inflammatory such as prednisone to provide instant relief from the itching.
If, however, you want to try to treat this at home first, you could use a benzoyl peroxide shampoo but make sure to condition afterwards (I recommend an oatmeal conditioner). You can get the shampoo at your veterinary hospital, or at a big pet store (PetSmart might have it) or on-line. Try shampoo/condition him once and see if there is any improvement. If there isn't, I suggest you take him to your veterinarian.
I'll give you some links:
example of Shampoo: http://www.allivet.com/DermaPet-Benzoyl-Peroxide-Plus-Shampoo-p/26935.htm
example of Conditioner: http://www.calvetsupply.com/index.asp?PageAction=VIEWPROD&ProdID=373
Also, you could try some BENADRYL (diphenhydramine). The dose that one generally gives is 1mg/lb. Is Rocky about 50lbs? It comes as 25 mg tablets, and if he is 50lbs, you may wish to give him TWO TABLETS. This can be repeated every 8 hours for 24-36h.
Here is more about Benadryl:
You should see some improvement within 30 minutes.
So, your excellent video and photos make me suspicious that Rocky has pyoderma. Given how itchy and red he is, I believe he is going to need a course of antibiotics and some prednisone to find relief and to resolve this problem. The discharge from his prepuce of the penis is likely because the infection has also spread in there - it should resolve with antibiotics. If you are not able to seek veterinary attention tomorrow, then you may wish to try the shampoo, conditioner and Benadryl to give him some measure of relief.
If this has been helpful, please "accept" my answer and leave feedback. I will still be here to provide more information if you need it.
Good luck with your dog!