The build up of dead skin cells mixed with congealed underarm deoderant, particularly aluminium based preperations.
This mixture then permanently stains the arm pit area of business shirts leaving a yellowish stain on white business shirts. Ironing the shirt sets this mixture permanently.
Furthermore, this 'pit rott' contains an accumulation of bodily secretions giving a pungent aroma of concentrated stale urine, specially when the garment is being ironed or worn on a warm day.
I could see Tony's pit rott when he raised his arms to flex his biceps, trying to impress the office admin girls. The problem was the bum stench and fecal stains under his arms was enough to make the girls gag