adverb British Informal.
Examples from the Web for slap-bang
In slap-bang fashion, they sailed right into the Tripolitans and captured, cutlass in hand, the three leading ones.Yankee Ships and Yankee Sailors: Tales of 1812|James Barnes
Workmen generally dine at slap-bang shops, and are often paid at tommy shops.The Slang Dictionary|John Camden Hotten
You know, Francis, if you do not drink your medicine, you will never see Slap-bang again.
Round after round he scrambled his way in, slap-bang, right and left, every hit tremendously sent home.Rodney Stone|Arthur Conan Doyle