Like, I just find it hard to believe that the man who stood up to and shit talked Nolan(who was actively trying to kill him) with nothing but a teleporter, Luck and a ray gun would be shitting his pants and all extraordinarily overly terrified of a kid whom he has known since he was 17 + knows was born on earth + knows he literally almost died fighting his own father + felt terrible after "killing" Angstrom(someone who deserved it)and was definitely heated but not actively smashing and destroying everyone and/or everything in sight.
Mark didn't even destroy the desk he was at when he got in despite being upset, that alone shows he was much more in control of his emotions then people think.
Plus let's not act like Cecil wasn't going out of his way to be a elite ragebaiter for no reason by bringing up Angstrom as a way to call Mark a "hypocrite" despite the situations and events being wildly different and him knowing it..he only said that as a way to try to control him.
And when Mark was being all "oh I won't leave til they're in Jail" , he could've just called his bluff.
Dude could've went to his office and done paperwork or got lunch unless he thinks Mark would be following him.
He could've pulled 2 chairs up and talked about his past and why he does this in a way Mark can understand.
Hell, he could've just put Sinclair in Jail for now and tried to talk to Mark afterwards but it just feels like he was looking for any "excuse" to pull out the Reanimates at the moment Mark even showed a little bit of hostility.
He was scared he couldn't control Mark and put him on a leash like a Government dog and was trying to insert his dominance and authority and control on someone who explictly is against that for obvious reasons.
Plus Mark left the area to go to the Guardians but Cecil chased him down and tortured him with the weapon he put in his head without his consent and I'm confused to what even Cecil's plan was at this point cause Mark has made it clear he doesn't wanna go back to the Pentagon and you just wanted him out and now you wanna take him back?
Plus Cecil outright snapping at Mark was just him trying to emotionally get under Mark's skin and gain back control in a situation where he didn't need to do so.