Used as an exclamation. Can be used in suprise, or in excitement. Is usually used when referring to something happening to someone else, as in a put-down.
From the phrase "Oh Bust!" which was used when
one party would verbally bust on another and the bystander would
say "Oh Bust". It has morphed from "Oh Bust" to "Oh Bus" to "Bus" to "Busticle", or "Oh Busticle".