Are there specific fonts that you are easily irritated with? Why?

There are times when I receive mails where the sender have used fonts that are not really that good. I prefer simple fonts for emails. Some of my students submit paperworks with fonts that are not really meant for written reports.

Comic sans is universally reviled as the biggest stinker. Look, it's own website dedicated to banning it!:
http://bancomicsans.com/home.html

Courier is awful. All the personality of a tax accountant.

I am personally more offended that the people that designed the WWW decided that (hyper)text would somehow be a great navigational device. Words are ideas, words are not 'design' and are not by nature able to imply their relevance or importance via physical or pixel space occupied.  Words are metadata for reality: reality is viewed visually, audibly, etc.

I hate Brush Script MT. Once, I made a wedding invitation using the font for it looks nice for the occasion. Unfortunately, the printed one  doesn't appear the same as it is on the screen. It ruined my design.

I hate any font that looks more like a picture than typeface.  Lot's of squiggles or other decorative effects shouldn't get in the way of reading a message!