This is the 10126th most frequent German word.
peinlicher
More embarrassing.
In this sentence, 'peinliche' describes the nature of the situation as being embarrassing for an individual.
Das war eine peinliche Situation für ihn.
That was an embarrassing situation for him.
Here, 'peinlicher' qualifies 'Fehler', indicating the mistake caused discomfort or awkwardness.
Ihr peinlicher Fehler führte zu einer langen Diskussion.
Her embarrassing mistake led to a long discussion.
The usage of 'peinlichen' in this sentence describes the memories as being associated with embarrassment.