I had the misfortune of eating one of these bitter Zucchini flowers. It was extremely bitter and I could not even swallow the single bite I took. But it was enough to make me sick for two days. I couldn't even drink plain water since it caused instant vomit and/or diarrhea. Those were some of the worst days I had ever been through.

The plant was from my own backyard, but it was stressed due to some insect / squirrel eating many leaves and buds. Possibly that triggered the plant to make the toxins that keep predators away.