Simple is a somewhat relative term. There are also sometimes consequences.
If you want to really HIDE it, as opposed to "look like" you're hiding it or blocking editing, then you'd need to have a separate Privilege Set (and Account) for yourself. Then, in other Privilege Sets set the Records, View to restrict access, using some data in that record as part of the calculation.
This will work, in all circumstances, to hide that record from others. It will also slow down many operations (for them), such as Finds and List views; because it would be testing every record on the fly to see, "Is it restricted?". So I have to ask, does this "special" record HAVE to be mixed into the regular data table? Could this data be moved into a 1-record-only table (where a View restriction speed loss would be insignificant)?
I see now that you say "use or modify". The term "use" is vague. If it is OK for them to SEE it, but not OK to EDIT it, then you could restrict the Edit access, instead of the View access. That has no real speed hit, except for "mass" data changes. This is a common method.
The "grayed out" could be done with Conditional Formatting. But it would need to be done on each field. Or on a background (non-enterable) field, which is easier, but not really "grayed out", as it would make only the background a different color.
Thanks for your reply. What I would like to do is restrict edit access to the record. I have no problem with having the record viewed. I do not want anyone to be able to edit the record. Can you tell me how I can accomplish this.