What about a product can irritate you?

hmmm? lets see...the dial until you win INPUT SELECTOR?! overshoots. undershoots. just doesnt stop! This is the sort of device that belongs on a safe and not a pre-amp. It may be odd, but in my ideal of an amp less is more. I would be happiest without a remote, indicator lights, and I prefer buttons to knobs where knobs are not necessary.

any unreliability.

When I had some Monster cables with their "turbine" connectors they loved to try to pull out the RCA's they were connected to. Gave those away to someone who I wasn't real enamored with - let them make his day!
Having black-on-black writing on the back of pre-pro's is always fun, as my close vision distance is getting more challenged by the day, and not having contrast on the input naming sorta completes the challenge. I got a couple of those miner style lamp headbands so I can make out the lettering.
Unreliable - Yamaha - my old DSP 3090 spent more time in the shop than my old Alfa Romeo, and Pioneer - I gave away my DV47 when it just decided to give up the ghost - too many times in the shop for that too. No more Yammie or Pioneer for me even for third or fourth systems.

My biggest are too-coarse or too-fine volume controls and tempermental remotes. The sticker on the CD edges also get to me so I echo Edesilva on that one.

I agree with Edesilva,that little strip of wonder tape on CDs drives me nuts !!!