Why this shot is everywhere
Rain on glass is one of the oldest tricks in cinematography because it does three jobs at once: it adds depth by putting something between the camera and the subject, it turns any point light into a bloom, and it justifies a face that is not perfectly lit. That combination is why the look survives being used constantly — it is doing structural work, not just decorating.
Getting the mood right
Start dark. A source photo with directional light and real shadow gives the glass something to break up; flat daylight portraits come out looking like a photo with rain stickers on top. If the neon reads too strong and swamps the face, re-run rather than adjusting the source — the balance between reflection and subject varies noticeably between takes.