grant application review request
Once you've been in a field for long enough, essentially every proposal and paper is from someone who you know personally to some degree. That's unavoidable and knowing someone does not, in itself, constitute a conflict of interest.

The question that the funding agency will want to know about is whether you feel conflicted in writing an honest and fair review -- or, maybe more importantly, whether an external observer might wonder whether you might be conflicted in writing an honest and fair review. In other words, do you (or might someone think that you do) stand to gain something by writing a good or bad review?

If you conclude that you might be biased, or that someone else might think that you're biased, then you should decline to review. Otherwise, there is no reason to decline a review just because you know the author.