I hate it when...

• People use "loose" instead of "lose", or "lose" when they really mean "loose". (I have even seen "You looser!")
  
  
• Some Singaporeans assume that everyone else will understand their unique brand of netspeak (mostly combined with Singlish too), even on international forums.
  
  
• People confuse "principal" with "principle". (I just googled "school" and "principle", and oh wow... This seems to be a far more common mistake than I thought.)
  
  
• People confuse "than" with "then".
  

But what I hate most of all is when people use "wad" in place of "what" (and*gasp* even "wadeva/wadever"). >_>

From dictionary.com,
wad
n.

1. A small mass of soft material, often folded or rolled, used for padding, stuffing, or packing.
2. A compressed ball, roll, or lump, as of tobacco or chewing gum.
3. 1. A plug, as of cloth or paper, used to retain a powder charge in a muzzleloading gun or cannon.
   2. A disk, as of felt or paper, used to keep the powder and shot in place in a shotgun cartridge.
4. Informal. A large amount: a wad of troubles.
5. Informal.
   1. A sizable roll of paper money.
   2. A considerable amount of money.