Chinese equivalent of "Oh Burn"
In the scenario that a third party witnessed an insult of others two, or someone try to lighthearted fight back a insult, maybe "雷死了"（lei2 si3 le) in Chinese can fit in. "雷" means Thunder.  "雷死了" means someone think it's somewhat funny unbelievable and be shocked. 

A longer version is "雷得外焦里嫩" (Lei2 De Wai4 Jiao1 Li3 Nen4), which means someone got attached by thunder and lightning, and he got BURNed outside, but inside is still tender (think case of  overfired BBQ...) Maybe a picture can help to explain this situation better (found on internet)