Never really got offended with people checking me. I always found it as a way to see what gear I could improve on. There are people out there better then me, so I should learn from them. Sending tells to someone complaining about their gear is rude though, even if it is true.

One time in FFXI I had a Warrior's Belt from Dynamis Valkurm, and another war sent me a /tell saying "Wow, a Warrior with a Warrior's Belt but no Amemet Mantle +1. Nice."