Taxes! Not taxes themselves, but the process of filling out the forms, doing the worksheets, addressings envelopes, checking to make sure you got everything, making sure you did them all right, mailing them off, crossing you fingers and hoping you didn't do any of it wrong...

Its a bit stressful, to say the least...
The fact that they took off that TeleTax service, that helped me do mine last year in about 5 minutes.
Procrastination...