Well, I guess that works... as long as size is up to 152.

I was working in C#.

Thank you for this insight, I've been debugging my code for 30 minutes trying to figure out why I'm getting a random "Y" in my tests even though the result clearly doesn't.

Now I know I can stop, because my code works as intended.

This Kata feels broken.

Input string: No offense but,
Your writing is among the worst I've ever read

My result: N ffns bt,
r wrtng s mng th wrst 'v vr rd

DisemvowelTest
MultilineString
  Expected string length 41 but was 42. Strings differ at index 11.
  Expected: "N ffns bt,\nr wrtng s mng th wrst 'v vr rd"
  But was:  "N ffns bt,\nYr wrtng s mng th wrst 'v vr rd"
  -----------------------^
at DisemvowelTest.MultilineString () [0x00000] in :0 

Input string: What are you, a communist?
My result: Wht r , cmmnst?

OneMoreForGoodMeasure
  Expected string length 16 but was 17. Strings differ at index 6.
  Expected: "Wht r ,  cmmnst?"
  But was:  "Wht r y,  cmmnst?"
  -----------------^
at DisemvowelTest.OneMoreForGoodMeasure () [0x00000] in :0 

First of all, since the letter Y can be regarded as both a vowel and a consonant in English you should explicitly exclude it in the instructions if you mean to accept it as a consonant in your tests.

Second, it seems (as already stated three weeks ago) that "Expected" and "But was" have been mixed up. Please fix to avoid confusion for future participants.