いやだ is often used in informal Japanese – in situtaions like, ‘No, I don’t want to do it!’ (dictionary – unpleasant, destestable, reluctant…)
The other day I heard a slightly different usage according to my Japanese friend – the extended いや～だ can also be used in the following situation:
A: “Your coffee is the greatest, B!”
It seems to be like an embarrassed reaction to the compliment. Right?