In a typical high school course, the complex physics of collisions is broken up into the dichotomy of perfectly elastic versus completely inelastic collisions. Real-life collisions, however, generally fall between these two extremes. An accurate treatment is still possible, as demonstrated in an investigation of coin collisions. Simple trigonometry is applied to Newton diagrams of the initial and final momenta. The transition from fully to partially elastic collisions entails a transformation from right triangles to obtuse triangles. Here, the deviation from the right angle is a measure of the relative energy loss. The evaluation of sliding distances independently confirms the trigonometric approach. A set of coin collisions is analyzed with respect to relative energy loss and internal consistency. The relevant data can be extracted from a single snapshot after the collision. The outcome of a complex collision is analyzed using simple geometric arguments and basic physics, making it well suited for high school students.