Interesting never heard of that yet but i will try this weekend.
Anyone doubting Koeman's commitment needs to read the below, a man of his beliefs, if we were Liverpool fans we'd have cr8p flags about this everywhere.
"We were at an away game once, having our pre-match meal. Our coach, Theo Verlangen, would go mad if he saw mayonnaise on our table. But this time he wasn’t paying attention when the waiter put some down in front of us.
Ronald (19) took a couple of chips, slapped them in the mayonnaise and just as he was about to eat them, Verlangen said: ‘Koeman! If you eat those, that’s a 500 guilder fine!’ Ronald stuffed them in his mouth and said: ‘Make it a thousand."