you do not get a yellow card for kneeling and heading the ball into the net. Kicking the ball away etc is bad sportsmanship. mouthing off too much is bad sportsmanship.
[MENTION=120240]mikescully[/MENTION] already provided an example: http://youtu.be/99LIG7olwiM?t=6m20s . That is, unless you're contending that a Superseries tournament does constitute a real match of any significance.
You have noticed this isn't a "real match of any significance"!? I'm pretty sure it has happened. And it has to be blown imho!! It's def worse than kicking the ball away as it shows so much disrepect for the opponent...
I'm surprised I haven't heard about it if it has happened. All sorts of things are against the rules but 'part of the game' now, e.g obstructing runners far away from the ball, holding in the area, leverage on peoples backs. All against the rules but never blown for.