So how do you tell your co worker that their speech is as boring as it could be? It is a delicate topic as most people do not like criticism and respond negatively to it. So your inclination to not want to point the boring aspect of their speech to your coworker is understandable, but you are doing them a disservice by not doing so.
What i recommend you to do is to record the colleague’s speech on a phone. Try to catch them during practice or maybe when he or she is giving a recurring speech, and record it to show it to them. Ask them to watch it together and figure out what is working and what is not. Show them, at least, the most boring parts of the presentation and their reaction will probably be of them realizing that they are, indeed, quite boring to listen to. Then, you can give them some constructive criticism. Tell them how they can incorporate stories and examples in their speech such as relevant case studies that can help strengthen your claims as well as make your speech way more interesting than before.
In this way, you get them to realize that they are boring and then give them a suggestion which can help them become a much better speaker.