A 55-year-old male presents to the ED for a rash of 2-day duration. He had URI symptoms for 4 days preceding the rash with myalgias and subjective fevers. He notes the rash began as small painless, erythematous papules but has progressed to larger, tender bullae. The rash began on his trunk and has spread to his face and bilateral upper extremities. He is febrile and tachycardic. On physical exam, the rash affects close to 20% of TBSA, and with gentle rubbing, skin sloughing is noted. What is the diagnosis?