Irregular reflection occurs due to: 

Reflection occurs when light rays from one medium touch the interface of two media, reverse direction, and return to the initial medium. The kind of surface or the contact between the two media determines the direction of the reflected rays. This allows us to distinguish between two forms of reflection: regular reflection and irregular reflection.
There are two kinds of reflection. The first type of reflection is regular, whereas the second type is irregular.
The reflection of light that occurs when it strikes a flat surface is known as regular reflection. When parallel light beams strike a smooth, flat surface, the reflected light rays follow the same path and are parallel to the incident light rays. This is typical introspection.

When light rays strike an uneven or non-uniform reflecting surface, irregular reflection results. Due to the non-uniformity of the surface, parallel light rays impinge from various directions and reflected from different directions. This sort of reflection is known as an irregular reflection because following reflection, the directions of all the parallel rays change.
Therefore, the reflecting surface's irregularity is what causes the uneven reflection.

Hence, the correct answer is option B.