Meaning:
“一首” (one) is a quantifier often used to modify a song or poem, “凉凉,” which literally means “chill,” refers to “Embracing the Chill,” a theme song of the popular Chinese TV series “Eternal Love,” and “送给” means to “give as a gift.” Chinese netizens jokingly use the saying to imply that something bad will happen to the person for whom this song is sung.
Example:
A: 下周就要交论文了，你写完了吗？
Xiàzhōu jiùyào jiāo lùnwén le，nǐ xiěwán le ma？
Next week comes the deadline to submit the paper. Have you finished writing it?
B: 快写完了，但不太满意，感觉很多地方需要改。
Kuài xiěwán le，dàn bú tài mǎnyì，gǎnjué hěnduō dìfāng xūyào gǎi。
Almost, but I’m not satisfied with my work and feel it needs rewriting in many places.
A: 那你还来看电影，一首《凉凉》送给你。
Nà nǐ hái lái kàn diànyǐng，yīshǒu 《liángliáng 》sòng gěi nǐ。
Yet you have come to see a movie. You’re doomed.
