Well acute behaviour changes may be due to stressors or life event or early sign of mood disorders.
When there r symptoms of mood swings n patient realises that these swings are spontaneous and non provocative without any relations to stressors means it's time to look for other biological functions like sleep, appetite and social n occupation functioning. If there is no changes in those functions, patient need to be observed n to initiate psychotherapy for ventilation. If there is disturbing functioning need immediate consultation.
Next Steps
discuss about his behaviour changes with other friends to verify its pervasiveness. if it's only with you them give him space n find out the reason.
Health Tips
Avoid all kind of situation which provokes irritability.