"A collection of insults 19" joke

His pointers are null / uninitialized.

His puzzle is missing a few pieces.

His reaction time is longer than his attention span. -- Thaves

His root file system isn't mounted.

His seat back is not in the full upright and locked position.

His shared libraries aren't installed.

His signal-to-noise ratio is epsilon.

His spark can't jump the gap.

His spirit guide is a three-toed sloth.

His stack's not very deep / he has an eight-byte stack.

His string's aren't null-terminated.

His strip is demagnetized.

His system administrator is never in.

His train tracks aren't quite parallel.

His URL denies outside access.