TP Karma is the resulting action from a person's decision that they are faced with upon using the last of the toilet paper. A person can either: a) replace the toilet paper, thus saving the next person the potential horror of being without, or b) leave it empty, selfishly moving on with your day.
If they choose the honorable decision 'A', the next time they stumble into a bathroom and the TP is all gone, they will immediately take note of it before going to the bathroom. Should the person make sinister decision 'B', then the next time they go into a bathroom without TP, they will carelessly plop down disregarding the supply (or lackthereof) of TP, not realizing until it is far too late to turn back.
a) After using the last of the roll, Joe lovingly replaces the empty roll with a fresh one. Later that day, Joe goes into a bathroom and sits down on a toilet, when all of the sudden his subconscience flashes: "Quick! Before you release, check the TP supply!" Joe turns his head only to find that it is empty. Luckily, he hasn't released yet, so he is able to comfortably walk out and grab a fresh roll.
b) After using the last of the roll, Suzanne walks out of the bathroom, thinking: "Whatever. The next person can get it". Later that day, Suzanne's intense diarrhea flares up, and she makes a beeline for the bathroom. Barely making it in on time, Suzanne pays no attention to the sparse TP reserves in the bathroom stall. When ready to wipe, Suzanne's eyes fix on the depleted roll of TP. It is then that Suzanne realizes that her bad TP Karma has caught up with her.