I'll give you some real life situations I encountered. You can make a conversation around them.
- flames during engine start
- fuel leaking from drain mast at engine
- gear pins still installed
- hatch on engine opened during start. I went to close it, so had to advise them to never touch the throttle. (I'm an engineer, ground crew would never go under a turning engine).
- beacon light not on during pushback (broken)
- tow bar shear pin broken, had to assess nose wheel damage on the spot.
- no EGT indication - return to stand
- entry door handle not flush with the outside skin, ask pilots to recycle the door
- cargo door fault light, pilot asks to recycle door