That guard dog story is one I heard many years ago, as a young grad. Told by a friend who went into beancounting the same time as I took my first hacking job. They were auditing someone who tried to claim dog food against tax. They (the auditors) had met the dogs in question in circumstances where a guard dog should've seen them off, and the dogs had been entirely friendly. They disallowed that claim.
As for the mother-in-law joke, that of course comes from an era of much more acute housing shortage than today's "crisis", when young couples would live for years on the mother-in-law's couch before they could get their own place. Naturally the mother-in-law walking in and out cramped a chap's style, and the classic joke was a safety-valve for pent up frustration.
What's this year's excuse? I just had a minor hiatus, where I'd lost all record of a modest (£200-ish) taxable commission-rebate payment. A simple 'phone call got me a copy of that from the rebater.