It's rarely easy to give constructive criticism. Even the best efforts might not always hit the mark, especially when dealing with a particularly sensitive person. When you have to criticize someone who doesn't take criticism well, you must strike a balance between being gentle on feelings and still being firm enough to get your point across and get results. Understand the mindset of a sensitive person and take a flexible approach to getting what you need.
Eager to Please
Understand from the outset that sensitive people are often eager to please, or at least unusually afraid of people being unhappy with them. What this means is that your criticism will pack a stronger punch with them than it does with many other people. Adjust the power of what you say accordingly. If anything, with a sensitive person you should try to err on the side of being too gentle, then try again more firmly if your point doesn't seem to be getting across.
If you can do so while still maintaining authenticity, reassure a sensitive person before delving into the criticism. Even if it's as simple as thanking her for her efforts and letting her know that you're happy with what she's doing overall, this reassurance will make her less likely to react badly to the criticism. Whenever possible, try to sneak in a proactive compliment to her for her ability to take constructive criticism well, such as, “I know and appreciate that you're willing to work on things to improve them, so...” Building her confidence will not only soften the blow of the criticism, it will help her feel that she's capable of tackling the changes you need.
In many cases, you can avoid triggering a sensitive person's insecurity by focusing on the language you use to make the criticism. Whenever you can, avoid “you” statements and use “I” or “we” statements. For example, instead of saying, “You need to do this differently,” say, “I'd like this done a little differently,” or, “I think we need something a bit different here.” Monitor your tone of voice carefully to eliminate any harsh, angry or critical tones and keep the sound upbeat.
Focus on Results
Remember that what ultimately matters is results. If you're dealing with a particularly sensitive person and don't think you can address the matter directly, brainstorm creative ways to send the message indirectly. This could mean asking him questions to lead him to realize the problem or, if possible, criticizing indirectly by directing the corrective statement at a group instead of an individual. Give him a chance to discover the solution for the problem himself by asking things like, “Do you think there's any way that...” in an earnest tone.