Hello,
That is not tail rot, but looks like it has gotten pinched in something possibly, or some retained
shed in that area. How long has it looked like this?
If it is retained shed it may work itself off or the very tip might dry up & fall off, it is hard to know
for sure. Just keep an eye on it, to be sure that it doesn't become discolored, etc & travel up the
tail.
Tracie