This is such a difficult question. We can, up to a point. We can change our behaviour and challenge our thoughts to try and help ourselves, but I don't think we can 'make' ourselves happy. Same thing with other people, to me, no, I don't think you can make others happy. And I've spent too much time trying, trying to console people in my family in particular. Trying to make them happy. I literally went to therapy partly because I wanted to help my mum. Which I thought would make me happy. But I think it's not your job to make people happy. You can sit with them, you can be there for them, you can distract them, but I don't think you can MAKE them happy. And if you can it takes a lot of energy and can be so burdening 
Yes, for me definitely. I don't want myself to be happy because I don't think I deserve to be. Or I think what's the point. And that can lead to avoidance and self-sabotaging behaviour. If there weren't times when we didn't want to make ourselves or others unhappy there would be a lot less suffering in the world. Unfortunately, yes we are human and there can definitely be times when we lose our cool, whether it be because of anger or hurt and wanting others to understand how they've hurt us. Or just we don't want to be the only ones who are unhappy. It happens. And that's okay. Because we all have been hurt and we all have hurt people (intentionally or not). Because we're human... I think we're hardwired to have all those emotions, like fear, anger, and sadness, that can lead us to do things we're not proud of. We just learn to manage them as we grow and learn. That's just my feeling about it though!
Ooh this is an interesting question! There are things we can definitely do to help regulate our emotions. For example, if we enjoy eating certain foods, then we can indulge in some tasty treats. And we can definitely make others happy! If we help others out, hang out with others and make them feel valued, they will appreciate your efforts. At the same time, I think I would be lying if I claimed to always make others happy 
Sometimes, we unintentionally say or do things to happen, and that's okay! And sometimes, we feel unhappy, and that's okay as well. Although I don't go out of my way to feel unhappy, I don't try my absolute hardest to be the happiest person ever. I allow myself to feel unhappiness if needed, and let myself feel happiness as well!
I mean less so nowadays but yeah I still get those knee jerk reactions of wanting revenge- I'm better at managing anger now though!Mm that's so true as well @WheresMySquishy
We have to maintain those boundaries and look after ourselves first
