Term commonly used in the Maritime provinces of Canada to describe the male genitals in a state of semi-arousal. Generally occurs as a pre-cursor to a full-out hard on, or after ejaculation, when you're hanging long and lazy.
In a hospital setting, it is when a male wearing scrubs is suddenly overwhelmed with an erection, largely due to a attractive female employee displaying her attributes on purpose or otherwise.
"Did you see that chick on 4 west?"
"Yeah! She's smokin', I got a chub in the scrub when she dropped her pen and bent over to pick it up!"