All I can suggest is to dig deep and pull up your inner mule. Be stubborn and consistent and eventually he'll either come around or at least accept that you've chosen to lead a healthier life and fully intent to eat healthy regardless of the example he's setting. I've been working on my mother for YEARS, dad however was pretty much a lost cause until he watched his own mother die. She didn't die from obesity, but I think a life time of a poor diet definitely contributed to her health problems. I think down deep dad knows this and he's made some progress, well my mother puts salad on the table now and he eats it without complaining (which by the way is new for him, he always complained before).
Maybe where your dad is concerned you could offer to do the grocery shopping or the cooking. A lot of men won't choose to eat healthy, but if you put hot food in front of them they will eat without question or complaints. A lot of healthy dishes are delish, so it shouldn't be that hard to get him to cooperate a little at least. Also arguing with him may only make him more stubborn, so as a tactic I can't recommend it. You might make a practice of reading the nutritional labels on his junk food, and should it come up be able to express your concerns.
Starting weight: 244.6 lbs. 10/01/09
Pounds lost: 80.6 lbs
Current weight: 164 lbs
Goal weight: 120 lbs
Weight to go: 44 lbs
Goal Date: 1/1/13