I just watched the Emmy Awards on television. The one thing I'm left thinking is how differently you end up thinking about the word "infectious" after you spend any time at all in a hospital. There was someone giving a speech, and she mentioned that the "everything about [the director] was infectious," and I couldn't help having the reaction that everyone ought to be staying away from him. The people near him in the audience should move, now, quickly, far away. The cast should not be complimenting him, they should be quarantining him, and figuring out how to best address whatever the problem is, and why everything about him was infectious. What is the infection, is there medication they should be taking, should they be wearing masks.... It's almost unfathomable that in normal usage, that is a good word, and means you're complimenting someone. Because nothing about it is good in the hospital. No one will ever happily say that anything about anyone is infectious.
And the worst thing I can imagine is an infectious laugh, because then you're just spewing whatever it is you have over everyone around you, and they don't even know when it's coming.