I’ve had this happen to me several times.

When you’ve just met a person, you’re still trying to figure out who they are.

They decide its good to reveal that they have a sarcastic personality and proceed to tell me something they think is so ridiculously outlandish that I will burst out laughing.

“Yeah.. because my parents are Christian Missionaries who are leaving for Australia tomorrow.”

Unless you say your sarcastic remark with a hilarious voice or facial expression, instead of the style of a deadpan sarcastic twat remark… why the hell would I assume you were being sarcastic.
Having Christian missionaries as parents is very believable.

The world can be a crazy place. Lots of unexpected things happen in life.
The temerity to now assume that I’m a gullible idiot who will believe anything because I didn’t catch your sarcasm?

“Well, if you knew me.. then you would know that what I just said was really funny.”

A lot of good that does when I’m just meeting you for the first time.