It is your responsibility to defend the Blessed Sacrament from profanation and scandal. You may either alert one of the ushers or question the person directly. Ask them to consume the Blessed Sacrament or return it to you. Remain until they have consumed it or return it. If there is any doubt or question, alert the priest.
Approach the altar after the priest has received from the chalice. Usually, you will hear a bell indicating it is time to approach the altar. If there is no bell, pay attention to when the altar servers begin to line up for Holy Communion and stand next to them.
A priest or deacon, or an extraordinary minister who takes the Most Holy Eucharist when an ordained minister is absent or impeded in order to administer it as Communion for a sick person, should go insofar as possible directly from the place where the Sacrament is reserved to the sick person’s home, leaving aside any profane business so that any danger of profanation may be avoided and the greatest reverence for the Body of Christ may be ensured. Additionally, it is improper to go to the tabernacle before Mass to obtain the Blessed Sacrament for a pyx and carry it throughout Mass. Furthermore the Rite for the administration of Communion to the sick, as prescribed in the Roman Ritual, is always to be used.