Misconceptions about dieting (roommate style)

When my roommate found out I was going on a diet for a week (this was a couple of weeks ago), I got the typical reaction: "Oh, I should lose some weight, too. I'm gonna do it with you. What does the diet look like?" So I told him that for a week, you basically live on fruit, vegetables, and salads with some healthy protein sources. Immediately, his face went blank and he backed out, because that is "hard" and he "can't do it".
First of all, duh!, you won't lose weight if you keep eating like you always do and/or don't work out more. And secondly, it's just for a week. Anyway, I stuck to my diet plan and it worked really well; I lost 2.5 kilos in seven days, and when I told my roommate, I got that very same "I should diet, too"-response. After that, he amused me almost every day with his misconceptions about dieting and excuses for him not getting it done right. Here are my personal highlights:
On the day he first found out how much I lost, he told me (filled with pride and a smug grin on his face) that he had only eaten a slice of toast for breakfast and then nothing else for most of the day. At that time, it was evening, and he was shoving junk food down his throat. It was so ridiculous that I forgot all about politeness and told him what I thought (not much appreciated, though). I said, dude, that's not how it works. It's not about eating less, it's mostly about eating healthier without making your body feel too hungry -> eat regularly. He was visibly disappointed that I wasn't impressed by his "dieting" and that I basically told him that his approach doesn't work. But that's not my fault, I think.

The next day, he holds up a bag of cereals he bought for his "diet". Unfortunately, it wasn't any kind of grain-y cereal, but chocolate puffs. I say it again, CHOCOLATE PUFFS. He tried to convince me that cereals are healthy, and that since chocolate puffs are in the cereal section of the supermarket, chocolate puffs are healthy and will therefore help him lose weight. This time I didn't bother speaking my mind, because it wouldn't make much of a difference anyway. But on the inside I was doubling over laughing at the thought that people are seriously convinced that chocolate puffs will help you lose weight. I mean, man, just take a look at the calories they list on the package. It has A LOT of calories and sugar and will make you crave more sugar.

The third highlight was when my roomie realized that I work out for at least an hour every day except Tuesdays. Again, he was all talk, no action. He said, yeah, he really needed to work out and he's even got a membership at some gym. The reason why he doesn't go: he doesn't have the right shoes. At that point, I was beyond commenting. You can get shoes for twenty bucks, it's not that difficult. And if you don't do hardcore training (which I assume he doesn't), you don't need the 150 euros pro-shoes, the cheaper ones will do just fine.

But this is my roommate. Sometimes I think he only says all these things so that I tell him he doesn't need to lose weight, looks good etc. But I'm not here to stroke his ego, and when it's not true, I'm not gonna say it just so that he can sit back and relax. I'm not telling him that he could use some diet and workout, either, don't get me wrong, I'm not that much of an asshole. But I won't lie.