You may have a disagreement with umpire on a decision made against you on a cricket field but, as a cricketer ~ you're not allowed to show your feelings to the umpire or any other player, specially those aggressive ones..
World watched Stuart Broad debate multiple times with umpire Billy Bowden who ruled against close lbw appeals on Sachin Tendulkar and Suresh Raina on last day of previous test but the smart thing Broad had done then was that he politely reminded New Zealander that he had made mistake. Today, Praveen Kumar of India went through similar rush of blood but couldn't keep his head like Broad had and was charged 20 percent of his match fee for dissent against umpre Marais Erasmus.
What actually happened was Praveen Kumar (PK) had trapped good friend but competitor Kevin Pietersen (KP) almost dead in front of stump in second hour of the morning's day, in the 18th over, but South African official ruled against visitors. Since there's no UDRS for lbw in this series, KP continued to bat, irking PK who engaged in a prolonged debate with Erasmus at the end of the over untill Rahul Dravid & Harbhajan Singh intervened and pulled their fast bowler away.
After the close of play, Praveen Kumar was found guilty of article 2.1.3 of ICC's code of conduct and match referee Ranjan Madhugalle fined him 20 percent of match fee when he pleaded guilty. had he not, punishment may have been severe. There was no warning given to Praveen Kumar who will put him in bad books of match referee only into his 5th test match in career.
The incidence, thankfully, soon vaporised off Praveen's mind as he made the crucial break-through after tea break and finished the day with 3 wickets in his kitty.