It's always been part of cricket for the players of one team to seek to unsettle an opponent. For example, crowding fielders ridiculously close around a tail-end batsman as he arrives at the crease is designed to make him nervous, as is a fast bowler firing a bouncer around his head with the first delivery he receives.
Similarly, if a batsman is coming up to significant point in a innings (such as 50 or 100) a good captain will always make him wait while the skipper goes through countless adjustments to the field so as to try to break the batsman's rhythm.
Such actions are regarded not only as acceptable but, indeed, commendable.
Sledging clearly takes things a bit further and the line between what is acceptable or not is a grey one. However any batsman with a reasonable amount of confidence should be able to take it in his stride.
Example:
Rodney Marsh to Ian Botham (as he arrived at the wicket): "So how's your wife and my kid's?"
Ian Botham: "Wife's fine. Kid's are retarded".
Even so, very few fielders in county or international cricket would consider distracting the batsman at the point of the bowler's delivery. As the saying goes: "It's simply not cricket, old bean!"
;-)