I don't want to lose my job but?

i've been working recently for a travel agency, the office i work in has been closed for about a month before i came, there was this old man who was working in it but he ad to stop for medical reasons but now he wants to get back, the manager made a deal with him that i stay from 8am to 5pm and he spend the rest of the day but he doesn't seem to approve, he keeps criticizing what i do, changes places of things purposely, and recently he told me that the office smells really bad, that was an insult right in the face, the office doesn't smell bad, i have air freshener, i spray it every half an hour all over the office and if he meant me i smell a looooooooooooooooot better than he does, talking to him isn't an option cause i'll end up kicking his sorry azz.........