A few come to mind pretty much immediately... all connected to bottle of drain cleaner I had to get today.
Products that are HARD to open... like liquids in containers where you have to push down on lid and turn at the same time.
Labels that are VERY hard to read. First, the instructions are MINUTE... thought I was gonna need a magnifying glass!?! Second, the print was in color on a colored background. Just one click larger and WHITE lettering on a DARK background woulda made things much easier.
Realize this is a bit product specific (cleaning stuff), but all or some of these gripes can be applied to stuff all over the house. I totally understand the need for stuff to be in tamper/child-proof containers or be sealed so they won't ooze out if product is on its side.