Wrong cases, apostrophe abuse, muddled contractions, lack of punctuation, capitalization...
Pet peeves, all of them.
Huge irritation: 'You guy's" pronounced 'you guyziz' as a possessive case statement.
's instead of 're in possessive case when referring to plural...
their they're there...
It's spelled 'SPEECH', not 'speach'. Cars use BRAKES to stop, not breaks...you don't want your car breaking in order to stop.
SuspenSion, not suspention.
'For SALE', not 'For sell.' Sell is a verb, sale is a noun.
Elimination of 'to be' in a sentence; 'It needs TO BE fixed', not 'It needs fixed'.
I swear, I want to beat people senseless with a dictionary and a 4th grade grammar book at times.
Look, my writing and speech isn't perfect, but there are set standards and proper forms of communication. Showing people that you care about their ability to understand you is done through attention to detail in your writing and verbal communication. It's called courtesy. The more you deviate from that set standard, the harder it is for others to understand you.