burst sb's bubble

burst sb's bubble
prick sb's bubble
(to ruin someone's fantasies; to bring an end to somebody's hopes, happiness, etc by making them realize that something is not as good as they thought it was; to disappoint with bad news, to tell someone unexpected bad news; to destroy someone's illusion or delusion; ) — обломать кайф (разг.); сообщить что-л. неприятное; портить (всю) обедню неприятным сообщением; выявить /показать / доказать и пр. бесполезность / пустоту/ бессмысленность/ ничтожность кого-л. или чего-л.; развенчать что-л. или кого-л.; лишить иллюзий
also
burst the bubble of sb

Example: I hate to burst your bubble, but she's playing you for a fool. I think she's cheating on you.

Example 2: He seemed so happy, I couldn't bear to burst his bubble so soon.

Example 3: I don't want to burst her bubble by telling her we won't have a vacation this summer. (thefreedictionary.com)

Example 4: I hate to burst your bubble, but Columbus did not discover Canada. (thefreedictionary.com)

Example 5: Even if you think I am being foolish, please don't burst my bubble. (thefreedictionary.com)

also burst the bubble of sb

Example: He tries to burst the bubble of anyone who believes population growth is not a problem. (thefreedictionary.com)

If someone bursts your bubble, they expose the faults in your plans or hopes. The image is of you blowing soap bubbles for fun, and someone comes along and pops them, ruining your fun.

Related vocabulary:
[rain on sb's parade]
[put a damper on sth]