Well irony for one, people often confuse it with sarcasm,
Semantics
Awesome (is it really fear inspiring?)
Bandwidth
There, Their, and They're - Really, it is not that difficult.
Weight- He ways 68kg - NO, he weighs 667.08N, his mass is 68kg
Heat v.s. temperature
Love - people use it too often
Legitimate - used too often
To, Two, Too - I want to tear people's arms off when they misuse these two terms...oh, wait, there is too too. (or if properly phrased "as well")
Ignorant
-aphobic - Mistaking fear for dislike
As well as many many more.