Learn English – canonic term for “the one whose birthday party is being celebrated”

Perhaps you are thinking of the word euphemism, which has senses “The use of a word or phrase to replace another with one that is considered less offensive, blunt or vulgar than the word or phrase it replaces” and “A word or phrase that is used to replace another in this way.”

Some words that are related to the topic (but probably don't quite fit the context of the question) are bowdlerize (“To remove or alter those parts of a text considered offensive, vulgar, or otherwise unseemly”), gentrify (“to renovate something, especially housing, to make it more appealing to the middle classes”), and expurgate (“To edit out rude, incorrect, offensive, useless, or otherwise undesirable information from a book, CD or other publication; to cleanse; to purge”).

Consider shock (Oxford Learner’s Dictionary):

[countable, usually singular, uncountable] a strong feeling of surprise as a result of something happening, especially something unpleasant; the event that causes this feeling

As you have a number of “unwelcome surprises” in your text I would reserve shock for the really bad ones. Here are some examples of actual use (my boldface):

Prokofiev had a shock waiting for him in Chicago regarding Oranges. After arriving in town on 31 October he wrote to Johnson requesting a meeting to settle their disagreement "peacefully." The letter he received in return on 2 November did not contain anything about an appointment, rather it bore the news that two weeks ago a telegram had been sent to him in France stating that Oranges had been canceled permanently.
[Stephen D. Press, Prokofiev’s Ballets for Diaghilev, 2006.]

Our return to England was homecoming in many ways, but there was a shock waiting for me when we reached the hotel at Rye. I was handed a cablegram: “Don't come home. I am in good hands. Mother.” The rest of the day was frantic. Heart Attack? Stroke? Paralysis?
[Doris McCarthy, Doris McCarthy: My Life, 2006.]