When does a topical gag stop being topical? And, maybe more importantly, when does a topical gag stop being funny? I've been thinking about this a lot lately, partly because nearly a year on I'm still hearing comedians do jokes about the sodden Jubilee Pageant and the sodding Olympics and partly because there are so many outlets for up-to-the-nanosecond satire that old jokes – even good ones that would have once had a few days to shine are in danger of becoming redundant more quickly than ever due to overexposure.