If you're so smart, young man…
…then tell me why skinless sausages don't fall apart.
This is one of those things that people say to try to make you look stupid and that what you know is of little relevance to real life. Doing a maths degree, this is a phrase spoken to me quite often.
Like all really easy questions, "why don't they fall apart?" is very hard to answer without thinking. It is my intention to set the record straight: contrary to the implication of the question, it is not the skin that keeps the sausage together. One could just as simply ask "why doesn't a burger fall apart?". It amounts to fundamentally the same question.
This explaination is often followed by "well, why do they put the skin on, then?". This is best answered with a withering look, followed by a brief explaination (in your most patronising voice) of how it makes it easier to get them into the right shape, how it affects the flavour, how you can add different ingredients without having to take into consideration how well it will stay together (large lumps of stuff and low meat content help it fall apart, binding agents such as egg, flour or breadcrumbs help it stick together) and how sausages were traditionally made with skins and tradition is hard to change.