Giving honest, useful feedback to a friend or colleague without damaging the relationship is a genuine skill, and the difference between feedback that helps and feedback that stings unnecessarily usually comes down to how it is framed and delivered, not whether it is honest.
Focus your feedback specifically on the behaviour or the actual work itself, never on the persons character or identity, since this section of your presentation is unclear lands very differently, and is far more actionable, than you are not a good presenter, which attacks who they are rather than what they did. Frame the feedback around your genuine intent to help them improve, and say so directly if it is useful to, since people generally receive feedback considerably better once they trust that your underlying motive is support rather than criticism for its own sake. Be specific and concretely actionable rather than vague, since a vague comment like this is not great gives someone nothing they can actually act on, while a specific one, such as the introduction does not clearly state your main point yet, gives them a clear, concrete thing to fix.
Balance honest, direct critique with genuine acknowledgment of what is actually working well, since feedback that is entirely negative tends to read as an attack rather than as help, even when every individual point in it is technically accurate. Choose a private, appropriate moment for feedback rather than delivering it publicly or in the heat of the moment, and it is worth briefly checking in afterward to see how they genuinely took it, since this shows continued care beyond just delivering the message itself.
Example: A student giving feedback on a friends project presentation focused specifically on which section felt unclear and why, paired it with genuine praise for what worked well, and delivered it privately rather than in front of the group, which the friend later said made the feedback feel genuinely helpful rather than like criticism.
One practical tip: Be specific and concrete about the exact behaviour or work, not the person, and pair honest critique with genuine acknowledgment of what is working, since feedback that is entirely negative reads as an attack even when every individual point in it happens to be accurate.