avoid using the word 'initialized' to talk about that non-reentrant-capable state of the mutex

src/libstd/thread/mod.rs

@@ -940,7 +940,7 @@ pub struct ThreadId(u64);
 impl ThreadId {
     // Generate a new unique thread ID.
     fn new() -> ThreadId {
-        // `GUARD` is never initialized fully, so it is UB to attempt to
+        // We never call `GUARD.init()`, so it is UB to attempt to
         // acquire this mutex reentrantly!
         static GUARD: mutex::Mutex = mutex::Mutex::new();
         static mut COUNTER: u64 = 0;