Don't get it? Why did the uke got offended when the uke said "I can repay their kindness b...

Lemme know too!

Basically, Yuri was taking a jab at Jiri because when the story started, Yuri helped a very drunk Jiri go back to his home but because Jiri was really drunk at that time, he made a (sexual) move on Yuri (hence the "repaying by making sexual advances" phrase) and this happened twice.

After those times tho, Jiri apologized and never approached Yuri the same way again. Maybe he thought that their relationship is now more professional so he got "offended"/sad that Yuri is still bringing it up after Jiri has apologized multiple times.