What's your best unconventional "blessing" like when people tell an actor "break a leg!"
In inpatient psychiatry I tell my coworkers "I hope your shift is mind-numbingly boring" or something similar (keyword being boring) because in my line of work, interesting (usually) = bad.
In electrical/computer/embedded engineering, we have a running gag that microchips work by trapping magic smoke inside, and when you do something wrong, you "let out" the magic smoke.