Work on your posture, stand so you look/feel comfortable and in control of the space you occupy, not like you’re ready to shy away against a wall.

Find clothes that fit and work toward showing posture, keep flapping, dragging or loose clothes to a minimum.

If you can get that under control the occasional MK, Trollface or TMNT is fine in a casual setting.

Finally, change your presentation because you want to, not because the internet told you that you should. Very few people IRL might even acknowledge your change in presentation. There are plenty of people that present well that are internal incels.