Just like on the internet, sometimes things in support groups can be "sensationalized" and cause worry where it isn't necessary. The whole "magnesium" issue is one of those things and it comes up every once in a while here.
No, you wouldn't want to drink a bottle of magnesium citrate before a surgical procedure or in case of severe constipation. That would probably make you quite weak. However, a big spinach salad or a peanut butter sandwich or any other food, eaten in normal quantities is likely fine. However, if you find that you consistently "crash" within a couple of hours of having a certain food, of course you should consider testing it out and perhaps eliminating it.
There really aren't any foods that should absolutely be eliminated. I LOVE an occasional gin and tonic. However, I find that they don't love me. The minute amount of quinine leaves me weak for a few days and it isn't worth it. It's happened the 3 out of 3 times I've tried in over the last 10 years. So, I just avoid it. Should everyone with MG? I have no idea, but probably not.
The straw thing is kind of silly, IMO. Unless you are sucking back a drink as fast as you can, I really don't see how that would be a problem, In fact, if you are THAT weak, you probably couldn't suck on a straw in the first place. I've found straws to be useful, especially when arms are weak and the simple act of lifting and tipping a glass up to my mouth is a chore. Again, your milage may vary (even day to day).
There are no absolutes with MG, except maybe that it's a real PITA!
Read, listen to others' stories, compare them to your own experiences and go from there!