@Anna Good question and thank you for asking!
- small font (that I can't quickly make bigger)
- decorative fonts (that I can't quickly change)
- low-contrast font+background
- busy (textured) background
- very wide lines + low inter-line spacing
- images relevant to the text that don't have alt text
- images not relevant to the text that aren't marked as such (wasted time trying to decipher them)
- surprise visual movement that distracts from text (fly-overs, "clever" scrolling animations, etc.)