Final answer:
The physical therapist should do active assisted exercises and wait for the pain to subside.
Step-by-step explanation:
The best course of action for the physical therapist to take when the patient complains of severe pain and irritability during a grade 2 inferior glide on the glenohumeral joint is to do active assisted exercises and wait for the pain to subside. This is because the severe pain and irritability indicate that the mobilization technique may be too aggressive for the patient at this time. By doing active assisted exercises and giving the patient time to recover, the therapist can gradually progress the treatment plan and avoid further aggravating the patient's symptoms.