A little background: I work for a large company in an office setting. My team is 5 people in two locations with only myself and a coworker at my location in a control room with ~50 others. I have been working for a long time and am very respected for my knowledge regarding our work. My coworker was trained by me and is still being mentored when we have overlap on our shifts. 

My coworker is on the same pay as me as we are covered by an enterprise agreement and there is no 'senior' position for me to move into currently. We work shifts that alternate weekly, either 4.30am-12.30pm or 12pm-8pm. My coworker has been here for about 5 months. My coworker has been viewed by management on multiple occasions to bludge through a shift on his phone. 

Basically our morning shift is meant to give a handover in the 30 minute overlap to the afternoon shift in order to complete work the early shift started but did not finish and to pass on important information (we support applications used in the control room so outages/issues need to be known/monitored). The handover is also meant for the afternoon shift to provide information to the morning sjfit but NOT work tasks (due to morning shift having important set work).

I came into work (early shift this week) and checked our handover document and there were 4 tasks on it for me which would take about an hour. I also checked the group mailbox and the three emails I had handed over the previous afternoon were all assigned back to me. We also have a new starter who is friends with my coworker who advised that he was watching live streams for most of his shift and chatting via messenger. Admittedly in one task the coworker was asking for assistance to learn a new task so I'm happy with that but the remaining three tasks were work he could've easily done as our afternoon shift does not have an assigned workload. 

I messaged my coworker to let him know that the handover is only meant to be informative for the morning shift as per our process set by our manager. I mentioned that our manager has been unhappy with any deviation from process lately and was simply giving an FYI to save his skin in the future (evening shift is fairly relaxed as you need to find work if none is handed over so management tries to monitor work completed during this time).

My coworker responded with a meme of a little girl rolling her eyes with the caption "When your coworker tries to act like your supervisor. Please Susan, act your wage". Now this panged me pretty hard as I have been the one to train and mentor this coworker and have made a huge effort to up-skill him to handle the role which in turn can justify a pay rise for us both (change of grade/reclassify position) which he seems to want a lot.

So, AITA for feeling disrespected? I simply wrote the information in the handover document and kept my headphones on for our 30 minute overlap yesterday then left without saying a word. 