perspiration / sweat / CL:滴[di1],頭|头[tou2],身[shen1] / to be speechless (out of helplessness, embarrassment etc) (Internet slang used as an interjection)
一辞莫赞
yī cí mò zàn
left speechless by sth perfect (idiom)
无言可对
wú yán kě duì
unable to reply (idiom) / left speechless / at a loss for words