That simulation is pretty cool, v2kkim, thanks for that!
Also, I only say almost never because it is technically possible for them to collide (of course) but has never been observed and likely never will be. The nature of star formation and galactic motion, not to mention the vastness of space between stars. Here's an example to illustrate how rare the event would be:
A typical star such as our sun has a radius of about 10^9 meters. The distance to the nearest stars is on the order of 5 light years, or about 10^16 meters. Imagine the sun to be a pea (radius of roughly .01m), then the nearest star is 100,000m (100km) away. This gives you an idea of the absolute improbability of two peas 100km away from each other colliding.