What does it mean?
This phrase means to laugh oneself to death or die laughing.
In other words, it means to laugh really hard, even hysterically, or simply to find something very funny and experience great joy.
Where does it come from?
Presumably, you would laugh yourself to death, because the more you laugh, the less you can breathe. So if you can’t stop laughing, you’ll die from it.
How is it used?
This colloquial phrase exists in three varieties.
Less commonly one would say “zum Totlachen”, as it sounds rather stiff.
However, the phrase “fast totgelacht” (almost laughed to death) or “halb totgelacht” (half laughed to death) are used quite frequently in colloquial speech.
“Die Komödie war zum Totlachen.”
“The comedy was really hilarious.”
“Ich habe mich fast totgelacht, als er ihr den Streich gespielt hat.”
“I almost died laughing when he played the practical joke on her.”
“Ich habe mich halb totgelacht bei der Satiresendung gestern Abend.”
“I laughed by head off last night during the satire show.”