My worst one was many years ago in Lajes Airport (TER) Terceira Island of Portugal
Made a mistake of picking SATA (S4) connecting flight from LIS to TER to YYZ with their A310.
The airport being small wasn't what bothered me, but there was a lack of any worthy food/restaurant..........WORST were the stupid plastic chairs.......no way u can spend 6+ hours there, that was bad......not sure if things have changed there after all these years!
Never again, i swore to myself !!