Do not eat bitter tasting courgettes! Fothergills say there is an issue with one of their varieties.
https://www.mr-fothergills.co.uk/Product-Recall-MRF/
However this does not account for all reports and the issue can occur in any variety especially if the plant becomes stressed. If you do eat some courgette and end up with an upset stomach, please go to A&E immediately.