I have had this happen to me once before , I was with a fill in cause my partner banged out . He comes in talking about what a Great night he had but he was so tired and didn't feel like doing anything today , but if we went and got some coffee he would be OK. Well , I am the type of person that if i cant trust you with my life I cant ride with you even if it is only for one shift. I guess my point is you never know what types of jobs you going to get on any given tour so hell don't even go out with that person just tell him to go home or you will have to take it to a higher level . If you happen to be the supervisor and this is not a regular thing tell him to go home and come back for the next tour .