I found a nice glitch, lol.

[CDan75]

While watching a demo, press "E" two times.
(Please don't patch it.)
(No fucks has to be given, just info.)

[Felix-The-Ghost]

Yeah it's fun. If you make walls solid the players still walk through them too.
edit:I remember not being able to figure out how to spectate again :/

[X-Ray_Dog]

Not really a glitch nor is it "nice" I would say. It's just another part of the game.

[Felix-The-Ghost]

Pretty sure it's a bug as you can't get out of it.

Edit: okay, so it's just E again. Although your camera is restricted to your spectate type -- makes it appear unintended.

Edit2: Now I remember what I was originally thinking of. While watching a demo, I was somehow able to spawn with the players, but I wasn't able to collect pickups or go back to spectating.

[Edward]

yeah you can see it in this video for example : Gibbed-Gema7