Customer complains that the deployed desktop app is slow at site x.
I check it out with users at site x, and indeed, it does have a delay when trying to connect to a share on a server.
Checks with users at site y and z, no issues.
After a bit of digging, the resolve of a DNS record is most likely the culprit.
Send the ticket to the customer network team to investigate.
Get it back after an hour.

"We have pinged the DNS name, and it responds fine, there must be a bug in the application".

Oh and also, I wrote this rant at work, in my head, with a lot more cursewords involed.