A satellite navigation system (satnav) that is shit because it has old or bad maps and/or software. It may have addresses missing, tell you to take routes that are no longer possible due to road changes or take so long to recalculate routes that you've already missed the turning.
Sorry I'm late. My shatnav didn't know about the new one way system.
How accurate one's aim is whilst on the shitter. Shatnavs do not work well in public toilets.
If you see skidmarks down the side of a toilet, the previous user's shatnav was poor.