There's this old Dutch saying that goes something like this:

"Wie boter op zijn hoofd heeft moet niet in de zon gaan staan."

When translated into English it becomes:

"If you have butter on your head you should not sit in the sun."

In Holland, having butter on your head is a reference to not having a clear conscience. And of course by going outside during a hot sunny day, the situation is aggravated without a doubt.

I still cannot figure out why someone would do something as ridiculous as putting butter on one's head - it doesn't make much sense to me.