The trick is knowing who you can be brutally honest to. My boss knows that I am, to put it mildly, a grumpy old* man that can use language that might make a sailor blush. He also knows that <issue> will get fixed after my rants.
His boss : I tread lightly… Once (after that bozo called me at 10 pm, while I was the worse for wear in a pub, for an issue he inflicted upon himself) I might have been a bit too “honest”… repercussions were limited to a stern talk with *his* boss, but I tried to avoid these nowadays.
* : old means mid-forties. Or about 82 if level of cynicism counts after 23 years as a sysadmin.