Two comments after a demonstration
1Jin watches a demonstration about repairing a bicycle bell. The opening explanation repeats information he already knows, so he feels bored. Later, the speaker shows an unexpected way to test the spring. Jin becomes interested and asks how the test works. His feelings change during the same demonstration.
2Afterward, Jin writes, 'I was boring during the opening explanation.' He intends to describe his own feeling, not his effect on other people. A partner points out that a person can be boring, but that would mean the person makes others feel bored. The sentence is possible English, yet it does not express Jin's intended message.
3Jin changes boring to bored and adds the reason. He also calls the later demonstration interesting because it attracts his attention. The speaker is an interesting person to listen to, even though one part of the talk was boring for Jin. A useful correction therefore asks both who experiences the feeling and what causes it, instead of sorting every person and every object into fixed endings.