Here are some lines thought would be fun
1) "Incoming cat 5 WAAAAAAAAAA"..... false alarm its just 5 cats"
2) "Heeey you,... pilot, time to put your big boots on its time"
3) "Mech pilot 48775-12rt-20 in violation of throwing underpants at other mechs how do you plead?
4) (make straining sounds to fit into the mech) "wooo this mech is tiny and yet so cosy aaah"
5) (make snoring sound) Rise and shine my metal chum (snores continues) Ergh
6) (Whispering) "Dont make a sound if they find us its over...... (fart sound) RUNNNNNN