Suppose we have a gas with collisions. The mean free path, $l$, is the average distance a particle travels before colliding with another particle. This is the average, but what is the probability distribution of collisions? It cannot be a Gaussian, because there can be no collisions with $x<0.$ It also cannot be a Poisson distribution, because the distance traveled, $x$, is a real number.
The answer to this question will clearly depend on the nature of interactions between the particles, the (effective) radius of the particles, etc. But I have not found any resource which answers this question from a simple starting point.