I cannot even fathom the sheer extent of how ridiculous this is.
As you noted, eating disorders are caused by far more complex physiological and psychological issues than the fact you're being observed by a boy!
So dumb. Soooooooo dumb, man. And a bit insulting towards sufferers by implying we would develop this illness based on the genders present at the lunch table. What the hell?
By the way - on the contrary - I find I actually eat more when with guys, compared to when I'm with girls. Because my natural appetite is very large (since I have a high metabolic rate and I'm very active and so on) and boys tend to match that great appetite, whereas girls (not to generalise, but just from what I'm observed) tend to eat less, I thus feel more comfortable satisfying my appetite properly when I'm with boys who do not hesitate to go back for that second serve either!
