Subhajit, I don't think you need to make this kind of clarification on GE.
I'm glad you commented on this, Gustavo. I share your sentiments completely. Subhajit, if you continue to make such totally unnecessary "clarifications" in the future, please expect them to be edited out. I will delete them without hesitation.
I think both tenses are possible. Considering the speaker met that person today, the past perfect would be appropriate to express past before past (I can't remember if I had met him any day before today). However, we can also regard this as a life experience, mainly because of the present modal "can," in which case the present perfect would be suitable.
I agree that both tenses are possible in this and similar contexts, where the speaker is talking about an experience in the very recent past which he believes himself to have had for possibly the first time. Generally, native speakers use the present perfect in these cases, though the past perfect is of course justifiable.
For example, if I am listening to a song for the first time, I may naturally and legitimately say, "I haven't heard this song before." Even after the song has finished playing, however, I may still naturally and legitimately use the present perfect perfect: "I haven't heard that song before."
Of course, it is possible and justifiable to use the past perfect in that context: "I hadn't heard that song before." I heard it a minute ago, and I hadn't heard it before that. The important thing to understand is that it is not necessary for the past perfect to replace the present perfect in such contexts.
- Hey mom, Today, I met a man named Sunil Das. He said he knew me and he said many things about me that were true. But I can't remember if I had met him/have met him before.
This context is much like the one I just described, even if more than one minute has elapsed. The point is that the experience is fresh; the time that is really under discussion is the present. That it occurred a number of hours ago is a technicality that doesn't govern the choice of tense. We are talking about today ("now").
To make the past perfect natural here, I would change "can't remember" to "couldn't remember," so that the remembering of which you speak is itself located in the past. Indeed, with "couldn't remember," the present perfect would be incorrect.
- I couldn't remember if I had met him before.