The quote 'Scandal is gossip made tedious by morality.' is by Oscar Wilde from Act 3 of his play 'Lady Windermere's Fan.' Wilde was an Irish dramatist, novelist, & poet (1854 - 1900) Many famous quotes are used in films and books. Basically, Wilde meant that for the upper classes in his time, gossip was a form of entertainment, just as it would be in Gossip Girl. Morality or self righteousness turns scandal into boring gossip, because the next day there'll be another scandal to talk about. Just look in any popular women's magazines, last week's scandals about Hollywood's stars is boring now, because there are new scandals to publish.

the word tedious there is trying to emphasize that morality is sort of a nuisance

gossip basically means rumor. when rumor/gossip is branded my moral ideas as disgraceful or humiliating, then it becomes a scandal