... you're sending an email and you choose to add words like 'cron' and 'grep' to the spellchecker's dictionary.

... you're writing a blog post (in North America) and you use single quotes where grammatical convention would dictate double quotes, but you dismiss grammatical convention thinking, "PHP would parse it fine either way."

... you're thinking you should adhere to the rule of three when writing a funny list like this, but then it occurs to you that you could argue the numbering started at 0, so 2 really equals 3.