I once bought a small tube of toothpaste for travel. I didn't really check what was allowed by the airport, I just bought what looked small enough. I arrived at the airport, went through security, traveled to my destination and used the toothpaste during the week I was away.

When I was set to return my toothpaste was flagged at the airport. It was "too big". I of course argued with the TSA agent that I had flown into this exact airport a week before with MORE toothpaste in the container than it had in it now. Of course there is no logic. Into the bin my mostly new toothpaste went.

I had a full sized tube of toothpaste that had maybe one squirt left in it, and the TSA agent made me throw it away because the labeled size was bigger than 3oz.