People just love to correct you on this one, don't they?
Oh, except… bad can also be used to describe verbs. Which one you use, bad or badly, will depend on the nature of the verb in the sentence.
Let's break it down:
- Action verbs describe actions. They take the adverb badly.
- Linking verbs describe a person's feelings or state of being. They take the adjective bad.
"After a hard bout of fifteen minutes on the elliptical, Tanner smells pretty bad and should probably remove himself from any and all public spaces."
In this example, Tanner isn't actively sniffing something. He himself smells bad, so he should probably go take a shower already. Febreze-ing his armpits won't cut it.
"Should I feel bad that I like a guy who has about as much intelligence as a rock?"
Here, the speaker is feeling an emotion, so bad is the right word, even if the dude in question may not be the right guy.
"It's a good thing the fender bender didn't end too badly because otherwise my dad might have grounded me for life."
The crash in this sentence had to end at some point, so the verb end is referring to an action. That means badly is the correct word for this sentence.