Bash meaning to strike with a blow dates from the 16th century and the OED says it derives from combining the words bang and smash. In the late 19th/early 20th century, if you went on a bash you were going on a drunken spree. From about the mid-20th century, this meaning evolved into a ‘do’ or a party. To have a bash or dash at something in the sense of making an attempt is from the early 20th century c.1925. To bash on is to continue doggedly and is British military slang from c.1940 that developed into bash on regardless, typifying the dogged spirit of the early days of World War II. Bash meaning to criticise verbally or in writing is from the mid-20th century c. 1948, as in the expression ‘ear bashing’, which is a verbal assault on the ears, or sometimes just tedious, garrulous chatter.