You've gotten some great advice here.
I'd also offer this advice - from someone who has an unhealthy father who HASN'T managed to stay skinny but still eats junk, and tries to impose - you're only ever going to get him to realize that you're serious by following through on what you say you're going to do. It takes willpower (a lot) and dedication, but he seems like the "Show, don't tell" type of person.
Whenever my Dad has treats laying out (it's usually fun-size candy bars at home), I don't say anything to him, but I just move it out of my arm's reach. If he says something, I tell him I just didn't want it near me. I'll ask him if he wants any and offer it to him, that usually shuts him up
If he offers me something, I'll just say "No, thank you." Don't offer reasoning - he doesn't have to hear your reasoning! - and if he asks why, just say "I don't want any right now." (Again, with the not offering reasoning). The thing about it is, if you offer your reasoning, you're giving him more with which to belittle you or argue with you about, if that's his M.O.
Also... something else it took me time to learn - recognize the GOOD things he does. It may feel like he "always" or "never" does something, but I try to avoid putting those words into an argument as I find they're usually not true. Maybe one time he DOES move the treats. Or maybe he DOES move his snacks to the cupboard if you ask. Something, anything, even if it's just not saying anything when you bring out your healthy snacks. Make sure you're recognizing those things even if you don't say it out loud at first, because it might help you to deal with your own reaction to him (Family members know how to push buttons!! And we know how to LET them!!) and temper it. Just my two cents, though. I don't know your family
We're here if you need to vent more!
Female, 31 years old, 5'4 1/2" tall
Starting weight 1/4/11 = 215.2 lbs.
Weight 10/22/14 = 175.0 (net: -40.2)
Last mini-goal: 175 lbs. REACHED 10/22/14 --REWARD: New wallet
Current min-goal: 170 lbs.
Next large goal: 165 lbs. by 12/25/2014
Lowest weight: 156.7 lbs.
150.2 lbs. <--- Official "Healthy BMI" weight
Estimated final goal: 130-140 lbs.
"You don't have to change your life today. You only need to change your day today."