No, standing between two mirrors used in the construction of gravitational wave detectors like VIRGO or LIGO would not stop the detection of gravitational waves. Gravitational waves are not ordinary waves like light or sound waves that can be physically obstructed. They are ripples in the fabric of spacetime itself, caused by the acceleration of massive objects.
The mirrors in detectors like VIRGO and LIGO are part of an interferometer setup that measures tiny changes in the distance between them. Gravitational waves passing through the interferometer cause minute length changes in the arms, which can be detected by the interference pattern of light that reflects between the mirrors.
Standing between the mirrors would only interrupt the light path, potentially causing a loss of signal. However, it would not prevent the detection of gravitational waves themselves. The gravitational waves would still propagate through spacetime, and if they are within the detector's sensitivity range, they would be detected despite any obstacles in the light path.