It's the comedy contagion that will not be curbed. With each year, Mrs Brown’s Boys seems to provoke an even angrier backlash, but this Christmas there were indications the public was at last coming around to the perspective of the many aghast critics who have decried the BBC1 smash, as a harbinger of humanity’s downfall. The tide, it would appear, is going out on Brendan O’Carroll ’s potty-mouthed alter ego. Two million fewer viewers tuned in to the 2018 seasonal special, compared with the equivalent tinsel extravaganza of 12 months previously. Mrs Brown duly limped in at number eight in the 25 December TV ratings, six places down on 2017, and well behind Michael McIntyre’s Big Christmas Show and the Strictly Come Dancing Christmas dispatch. It really did have the stuffing knocked out of it.Yet the knockabout, merrily lowbrow Christmas episode was no better or worse than any previous Mrs Brown . Whatever else, O’Carroll cannot be accused of inconsistency. Could it be viewers simply have had their fill of single entendres, fnar-fnar nudges and a studio set almost as wooden as the acting by O’Carroll’s extended-family ensemble?For monthAs if anticipating the slump, the New Year ‘s Day broadcast is notably less crude. This is, in fact, one of the sweeter Mrs Brown's . Neighbourhood ne’er-do-well Buster Brady (Danny O’Carroll) must come to terms with a fatherhood bombshell while matriarch Agnes Brown is asked to deliver a funeral eulogy for a woman she barely remembers. Adding to her woes, sparks fly as best pal Winnie (Eilish O’Carroll) moves in with the Browns after her own house floods. O’Carroll and company tug unashamedly at the heart strings. Buster’s friends quickly work out that he can’t be the real father, but can’t bear to tell him. Agnes concludes she should have made more of an effort to get to know “Fat Belly Nelly” while she was alive. Along with the swearing and the toilet chortles, it is a reminder O’Carroll’s blockbuster has always had elephant-tranquilising levels of saccharine swirling through its veins. What the episode doesn’t particularly help to explain is O’Carroll’s superlative success since parachuting in from cult status in Ireland to become a goliath of British chuckledom. The obvious diagnosis is that the F-bombs and the genitalia jokes have filled a void in the market for honest, uncomplicated humour. Mrs Brown's Boys thrives not on snideness or superiority, but speaks to the universal truth that quite a lot of people enjoy fart gags. O’Carroll’s outsider status surely isn’t a factor. His humour exists in its own substratum and is indeed perhaps more in a British than Irish tradition of working men’s club comedy. Certainly back in his native Dublin, the consensus is that in exporting his Carry On -style shenanigans to the UK he is essentially flogging combustive sedimentary rocks to Newcastle. Maybe it’s the lack of clever-cleverness. Mrs Brown's Boys is a conveyor belt of victimless giggles which are coarse but never cruel. As the New Year’s Day baby Buster storyline underscores, it’s unapologetically soppy too. A dirty mouth and a big heart have combined to make Mrs Brown a sensation. And if the novelty is finally wearing thin, the fact that O’Carroll has spun remarkable ratings from such base material is nonetheless an achievement that deserves acknowledgement.