Why is my BD soo angry!!!! T_T?

OK so i have a 6 or 7 month old BD hes about a foot long and yeah i paid 5 dollars for him lol cause i adopted him from petco. ppl there were kinda sad to see him go cause hes bee there pretty Much his whole life and he was on display for maybe a month before his shoulder got broke (which is a complete mystery) and was taken to the vet were he was treated for his wounds. but know hes become a family member and i really love jak and im doing everything to keep him happy. but recently i read that is a good idea to bathe your beardie so ive started bathing him in my tub hes ok at first it really helped him potty but for the most part he really seems to hate the tub but i also read to keep doing it even if he doesnt like it! and since i gave him his last bath he hasnt bit me but he has puffed up big and hissed at me and i think hes angry which my grampa thinks is funny as hell buthes never done that till after his last bath he started running from m y hands soo i was just wondering what to do to get him...a lil less angry with me.