B&G acting up!

Ok so I Have had Tango since he was a baby, now is is 2 years and some change. Primarily it is my girlfriend and I that play with him and take care of him, with us he is good and has his bratty moments like any other bird! I currently still live at home with my parents. For the first year and a half Tango and my dad were best buds, my dad works at home so he would be home while I was gone at my job. He would go in the room with tango probably 3+ times a week during the day, take him out scratch his head give him a nut do whatever with him for the most part. The past 6 moths tango has gotten VERY nasty with my dad, not letting him near him without lunging at him. My dad has been super busy with work and has not been up to see tango anywhere near what he would if at all which was one idea I had with the problem. I know 100% he has never hit tango but I know that there are times tango will scream for a half hour nonstop and my dad will yell up to him.
The second possible idea is the way my dad tries to pet him, which is that he VERY cautiously gets his hand close to tango before trying to pet him. And when he does pet him he does it a little rough sometimes but not every time he tries.
Tango is also starting to be nasty with everyone besides my girlfriend and I, I know that is partially because we don't always have him around allot of people.

I would like some advice on the issue with my dad primarily, like things I could do for the issue and things my dad could try alone with tango. And some advice on trying to make tango more social I want people to look like this when they look at and pet tango not this please help! and thank you!!