Barney Calhoun

When the player is about to invade the Citadel, Barney's parting words are partly obscured by a heavy crash caused by Dog, resulting in "If you see Dr. Breen tell him I said fu- *CRASH!* -ou!" The crashing sound isn't part of the audio file for Barney's dialogue though, so the line can be heard in full in the game's files. Barney's voice actor even said the "fuck" part softly so that the crash would completely mute it out.

Example of:
Sound-Effect Bleep