Stack sizes:
BB: 2
MP: $100
CO: $200
me on button : $160

I have [7s][8s][9c] OTB.
MP minraises, CO calls, I raise pot, BB shortie pushes, all call, since shortie is on Monkey tilt and could have anything (Yes, maybe limping would have been better given that, but I can't help myself).

Flop (1 allin, main pot=$95): [9d][Qs]. Checked around.

Turn: . Checked to me. I pot into the empty sidepot (?!). Both fold.

+EV or not? My read on MP was that he was a bit of a loose cannon but not totally irrational; CO seemed to be reasonably decent lag.
Would it be better to make a smaller bet to build the sidepot since we're in position and seem to have the best hand or should we be content to get HU with shortie?

I like your play.

Since no one seems to have the straight (except maybe shorty), you probably have the best hand at this point. I see no need to let them draw for free to possible broadway straights or J-high flushes or such. A smaller bet also seems to me a bit contrived.

Definitely a bet but I'm undecided on the amount. Probably had to be there which means you probably made the right decision. I think you're okay to trust your judgement here.