I’ve never really set a quantified “too heavy” metric for myself. A knife can be heavy, but carry very well, due to dimension, shape, clip style, clip placement, and other factors. Some are indeed straight up bricks. I personally appreciate at least a certain amount of noticeable heft, because I don’t want to forget a knife is in my pocket, or realize far too late that it isn’t when it should be. My perspective might be somewhat skewed, though, since my work dictates wearing a lot of equipment, and anything I carry off duty is usually far lighter than anything I had to carry at work. That said, even if I’m not working, I’m usually wearing a belt.
One particular comfort issue I recall having was with a ZT0909. Yes, a relatively heavy knife, but it wasn’t the weight that bothered me about it. I REALLY wanted it to work for me as I loved everything EXCEPT the corners of the hex nut pivot, which irritated the heck out of my thigh through the fabric of my pants pockets. Man, a domed or countersunk pivot would have made that particular model downright ideal for me, even though it is heavy by a lot of folks’ standards at 7.5 oz.