Are some real world compression algorithms sometimes producing unexpectedly large files?
If you take vanilla RLE in bitmap which does not have any consecutive runs it will increase file size two times. It is apparently very rarely used fact that BMP, TIFF and PCX allows compression, (not all applications supporting these formats even implement RLE scheme). This is very pathological case and since it mostly increase file size it is abandoned.

Normal compression algorithms include information of failure, so instead of huge increase you can expect several bytes per chunk increase. In those that do not check there are three methods of checking how far we can increase file: take already compressed file, take encrypted file or find pathological cases from algorithm.

I have generated $256 \text{ bytes}$ file with consecutive numbers.
Compressed as 7z LZMA: $349 \text{ bytes}$, LZMA2:$356 \text{ bytes}$, Deflate or Deflate64: $400 \text{ bytes}$, bz2: $388 \text{ bytes}$, PPMd: $421 \text{ bytes}$ so not that cool.