Grammar

When you see a sign, which is grammatically incorrect, which ones irritate you the most

Seeing apostrophes in plurals.
I was in an office one day and saw a poster which told us what happened on each day of the week
It had apostrophes in plurals
Monday's Tuesday's and son on
I had to sit down with a glass of water and recover.

The one that gets me when I am in Morrisons's
10 items or less - it should be 10 items or fewer

Generally, the rule is if the noun is countable or uncountable