The first one to grab the heavy end of the couch is the leader, whatever the title says.

Leadership turns up before any title does, in who moves first when something unpleasant needs doing. People decide who they will follow by watching that rather than by reading a list of roles. Authority earned this way is given freely and is much harder to lose. Willingness is the actual credential.

Find the least appealing part of the next shared task and take it without discussion. Do not narrate it while you do it. Notice how differently people deal with you afterward.