I'll bear it in mind
What it really means
Literally "I will remember your suggestion". In practice it often means the person has politely noted your idea but will probably not act on it. If they ask follow-up questions, they may actually be interested.
Context, tips & common mistakes
"I'll bear it in mind" files your suggestion in a cabinet that is rarely reopened — it acknowledges without committing, and most of the time it politely means 'probably not'. Its cousins: 'noted', 'food for thought', 'worth considering'. None of them are promises; all of them end the topic gracefully.
If you actually need the thing considered, convert vagueness into specifics on the spot: 'thanks — shall I send you the details so you can decide by Friday?' A genuine yes engages with the deadline; a soft no produces another deferral, and now you know. Using the phrase yourself is legitimate — it is kinder than instant rejection — but with people who depend on your answer, follow up with the real decision rather than letting silence deliver it.