a foolish braggart
true origin is a comedy by Nicholas Udall called "Ralph Roister Doister" written a.1553
Roister Doister is my name,
A lusty brute I am the same
bit of a "player"; generally with women but can also be used in business. Origins - Only Fools and Horses.
"Rodders, I'd never of guessed, you ol' roister doister."