One example of a humorous sarcastic saying is, "If you're having trouble laughing at yourself, I have no problem doing it for you." Another example is, "Oh, I have had an amazing night," followed by a pause and then, "However, tonight wasn't that night."
A funny but sarcastic response to someone's nonstop complaining about how he hates his job is, "Let me introduce you to a support group for people like you. The name of the group is 'Everybody on the Planet,' and it meets regularly at the bar on Saturdays." The implication of the sarcastic response is that, although the person seems to think his disdain for his job makes him unique, his situation is not unique at all because there are plenty of other people in the world who have the same problem. Instead of acting like they have the worst lives ever, those people go to bars at the end of the work week to relieve stress.
A religious-themed sarcastic saying is, "I prayed every night for God to give me my very own guitar as a child, until one day, it dawned on me, that God didn't work like that. The next day, I stole a guitar and prayed for God's forgiveness." This saying pokes fun at the idea that it is wrong to engage in sinful behaviors, such as theft, but doing so is no big deal if one asks for forgiveness afterward.