My boy is the same age and also looks for opportunities to flex his authority. I made up my mind not to let these conflicts escalate into fights or to make threats that I either can't follow through with or that would be worse than just skipping the vest and doing manual CPT that time. I've only got a few hours a day with him when I get home from work so I just can't bear spending part of it angry at each other.
Usually what happens when he's in a mood to battle is that we have a verbal back and forth for awhile and I drop it for a half hour or so and play with him; then I just get the gear set up and lay out the vest on his chair in front of the TV (his usual mode of vest treatments) and lead him into it with no further discussion except perhaps telling him something like "what show do you want to watch?" or "we're doing the vest now and after it's done, what do you want for snack/dinner/etc". This works most of the time, but when it doesn't I either wait and try again a bit later or if time is running short I'll chase him down and do manual CPT - which he does not like any more, so most of the time it's enough to convince him to go back to the vest.
good luck.
Usually what happens when he's in a mood to battle is that we have a verbal back and forth for awhile and I drop it for a half hour or so and play with him; then I just get the gear set up and lay out the vest on his chair in front of the TV (his usual mode of vest treatments) and lead him into it with no further discussion except perhaps telling him something like "what show do you want to watch?" or "we're doing the vest now and after it's done, what do you want for snack/dinner/etc". This works most of the time, but when it doesn't I either wait and try again a bit later or if time is running short I'll chase him down and do manual CPT - which he does not like any more, so most of the time it's enough to convince him to go back to the vest.
good luck.