Sweatheart. It does it every time.
I don't know if this counts, but I use swype to text and when I started graduate school my dad texted me to ask if I needed any school supplies because he was out shopping at the time. i texted back "I don't have any penis". I meant pens. He asked me if I needed him to take me to the hospital.
One time I managed to type "snar" instead of "sense". I'm not quite sure how it happened, but snar has become a regular word in my vocabulary.
Llolz. My friend used this in a skype convo, and we adopted it as an inside joke. We say llama llolz.
taht and teh lol
I have a bad habit of writing 'shit' instead of 'shut', just because I'm a vulgar person... But it results in a lot of doors getting shat. I once wrote "Gideon climbed into his car and shit the door." My sister's response? "OH MY GOD! GIDEON NO! YOUR ASS! IT'S RUINED!"
It's fun to put a proper name into Microsoft Word and see what its spellchecker comes up with. For example, the name "Zarzecki" used to produce "carsick." (It doesn't any more. Shucky darn.)
It's fun to put -ers at the end of words. Yuppers. Nopers. Honeybunchers.
It's fun to put -ie at the end of words, as Amy Farrah Fowler (Mayim Bialik) does with "bestie."
Earlier today I encountered an article which declared that "the end is neigh", which might be the cutest mistake I've ever seen.
i work for a major retailer and we have signs everywhere listing products and the prices on them. someone once decided to make a new sign for some aprons however they failed to spell check it and ended up posting a sign for apeporn . . . yeah that one came down quick!
The two worst typos I ever (nearly) missed:
"Abrasion is when waves pelt the cliff face with rocks", is the correct version of a part of my GCSE geography work, only it came out as "abrasion is when waves pelt the cliff face with cocks".
"This caused massive public outcry", is what I meant in my GCSE history work, but it came out as "This caused massive pubic outcry".
My handwriting fails :(
There is a word that I will probably always spell incorrectly. Definitely. I always spell it "definately." I was an English major and am now an English teacher. Yet I think that this is one error that is here to stay in my internal dictionary.
the one i do most often is taht... even my laptop yells at me and changes it automatically...
off topic: when a bug flies close to your face and you think it's huge but then it's tiny, but by that time you've already screamed and people are staring... not like i care ;)