A bad speech can be bad in two ways.
It all depends on how you define bad.
Bad can mean of inferior quality, or defective, failing to measure up to standards, unpleasing, or unable to perform as required.
Think of a bad wine, or a bad movie, or a bad performance.
A bad speech, using this definition of bad, is ineffective. It fails to accomplish its objective.
A speech can be bad for any number of reasons:
- It lacks unity and cohesion.
- It fails to address the needs and concerns of the audience.
- It is confusing, illogical, or boring.
- It relies on poorly designed visual aids or fails to use them when appropriate.
- It is poorly staged and delivered.
Bad can also mean morally deficient, repugnant, evil, wrong.
We often shy away from using bad in this sense, afraid of sounding judgmental or ceding the term to preachers and pundits who see evil everywhere they look.
But I think that some ideas—many ideas—are bad and deserve to be labelled as such.
If an idea can be bad—immoral, reprehensible, worthy of censure—a speech that advocates it is, by extension, bad.
I hate to go there, but Hitler is the best example of what I mean.
His speeches were good in the sense that they achieved their objective. And they were bad—demonstratively and monstrously evil—because the ideas they advocated so effectively were bad.
To judge a speech in this sense—to weight its moral worth—requires us to clarify our values and the way we determine right and wrong.
When I think of a bad speech, in this sense, I think of one that distorts the truth, plays on an audience’s prejudices, focuses their attention on trivialities, justifies injustice, and targets the weak and vulnerable.
What do you think makes a bad speech bad?

As for me, I believe that any speech can be bad if you don’t pay attention to its logic. No matter how good at the topic you are, you might miss a logic structure once speech anxiety strikes you. If you’re interested what presentation logic is, read more here: http://presentationskills.me/logic/
And there is one actionable way out – the more you practice, the more prepared you are. If your speech is logical and structural, full of examples and interesting data, you can achieve success and stand out from other speakers!
Lale, Great ideas and great suggestions. I agree with you on every point.
Chris