It is definitely true that “whatever a man sows, that he will also reap” (Gal. 6:7). It is true agriculturally, and it is true personally. This works in two directions: one can reap good from some good he has sown, and one can reap evil from some evil he has sown. When we see someone “reap the evil that he had coming,” sometimes we might get a charge out of that and perhaps “enjoy” that he finally got his comeuppance. But, is that a 
Christian response?
A child of God is to have “agape love” for all mankind–Christians (1 John 4:7) and non-Christians (Matt. 22:39) alike, even our enemies (Matt. 5:44). Agape love seeks what is best and most needed by the one to whom we extend that Christian love. A Christian who has agape love for all people could hardly “rejoice” at the calamity of others (cf. 1 Cor. 13:4-6). The wise man wrote, “He who is glad at calamity will not go unpunished” (Prov. 17:5). Then, “Do not rejoice when your enemy falls, And do not let your heart be glad when he stumbles; Lest the Lord see it, and it displease Him” (Prov. 24:17-18). So, to snicker or not to snicker?