trackie-daks are the bottom half of the tracksuit, not the whole. the whole tracksuit is the trackie; the pants are the trackie-daks. but Random's example is unsurpassable :)
When two people really have to use the bathroom and there is only one available, they run to the toilet and wrestle for use of the bowl until someone is able to get their bare butt firmly situated on the seat. The first person to do this is the winner of the toilet tackle and is able to use the toilet before the other person (a critical move when both parties need to do a number two).