^True. While she may have changed her mind, I'm pretty sure that the Doctor hadn't. He was clearly so glad to be rid of her in "Time-Flight" and it's incredible to see his grimace as Nyssa invites her to rejoin them in "Arc of Infinity." It kinda seemed like the only reason why he added Turlough & Kameleon as companions was because he was hoping that they would annoy Tegan enough that she would leave because the 5th Doctor was too milquetoast to get rid of her himself. I kinda suspect that's why his next regeneration was so rude. The 5th Doctor was too easily pushed around, so he decided to become the kind of guy who wouldn't hesitate to tell people to f--k off if he wanted.
That seems pretty irresponsible. When the doors opened while the TARDIS was in flight, it created a vortex that nearly sucked out everyone in "The Enemy of the World." And when the doors opened while landing, it made the TARDIS shrink in "Planet of Giants."
I presume it was just an empty threat, like when he said he was going to spank Susan.