"Serene" is among the adjectives most frequently deployed when describing Pope Francis. It seems, however, that even the pontiff has his limits.Francis, who is on a five-day trip to Mexico, was greeting fans at a stadium in the city of Morella on Tuesday when he lost his cool with overzealous well-wishers.Following a colourful encounter with young dancers and singers, the pope went over to greet the faithful, at which point two arms reached out to grab him.The person, who is not seen in the video footage, did not let go, even after the pope lost his balance and fell onto a child in a wheelchair.After aides and security men stopped the pope from falling to the ground, a flash of anger crossed his face as he stood upright.Staring at the person, he raised his voice and said twice in Spanish: "Don't be selfish!"Francis then took a couple of steps back as appeals came over the public address system asking the crowd not to clump together.The Argentinian pope has tried to get closer to the public, opting to use open-top cars instead of a bullet-proof Popemobile used by his predecessors."It's true that anything could happen, but let's face it, at my age I don't have much to lose," he said two years ago.Francis was due to wrap up his trip to Mexico yesterday with some of his most anticipated events: a visit in a Ciudad Juarez prison just days after a riot in another lockup killed 49 inmates and a stop at the Texas border where immigration is a hot issue for the US presidential campaign.Republican presidential candidate Donald Trump has criticised the pope's plan to visit the border wall that separates Ciudad Juarez from El Paso, Texas, to put a focus on the plight of migrants...