Is it safe to re-heat food twice in a short time span? Imagine the following scenario. You make some food, and put part of it in the fridge relatively quickly (often before I eat, so I save e.g. half for later).
Some time later, usually dinner the same day, or either lunch or dinner the next day, I re-heat that food.
So far, so good, I assume.

Now, the question is: what if I re-heat it (first time) for dinner, but it gets cold while eating, and I re-heat it the second time perhaps 20-60 minutes later?

A, is it safe at all, and B, if it can be, do I have to heat it to cooking temperature yet again, or can I simply heat it so it's pleasant to eat, this second time? I always heat it properly the first time around.
The real issue is the total time it spends in the "danger zone" (40-140 F, 4-60 C), not how many times it is heated, frozen or refrigerated.  Those things may change the quality and make the food unpleasant, but that is a separate issue.  Re-heating in and of itself is not inherently unsafe.

See also:

How do I know if food left at room temperature is still safe to eat?