Chanyeol is tired of seeing Jongdae being taken for granted. Kyungsoo hates to admit, but for the benefit of the doubt-- he 'may'  have always liked it when Chanyeol goes out of his way just to bother him.

Baekhyun insists that he's jealous of Jongdae just because he's his 'best friend'. Kyungsoo knows otherwise, so he thinks of making Baekhyun jealous as his revenge-in-disguise to all the trouble Baekhyun's stupidity has caused him.