Perfect Timing.
The funniest thing I have ever seen a dog do was not a trick he learned or anything else but the most hilarious of coincidences.
My family used to have a black labrador who was a retired Guiding Eyes dog and he was by far the most mellow and gentle labrador I have ever been around. He loved to sidle up to people and lure them closer to his face by wagging his tail and leaning on them until they got close enough for him to saturate their face in drooly and foul-smelling kisses.
One day at my parents' house we were having a BBQ with some friends from church and we were all sitting on our back porch enjoying a warm July evening. I was sitting near my sister and another teenage boy whom my sister had a crush on at the time. As we were sitting there, our loving labrador (his name was Salem) cuddled up next to my sister and began to wag his tail and be absolutely adorable in order to get her attention. Of course it worked and my sister began to pat his head and accept his well-meaning kisses. Since her crush was sitting nearby, my sister was of course making a little bit of a display of the whole thing and demonstrating just how tender and kind she could be to animals.
After one or two kisses, Salem looked at my sister, took a step back, and emptied the contents of his stomach on our back porch. The absolute mortification on my sister's face, accompanied by an apologetic look on Salem's face made both me and my sister's crush fall of the porch from laughing.
Sadly, I don't think my sister ever got a chance to redeem her kissing skills with her crush.