You absolutely can ridicule someone’s lack of competence, for sure, because competence isn’t an inherent trait. Intelligence and competence aren’t really causally linked. Sure, someone with an intellectual disability might not be the world’s greatest chess player, for example, but for most people with an intellectual disability, with more than an average amount of practice, they can beat an average player.

I think “tripped over his own dick” is fine, that doesn’t suggest to me “he’s bad because he has mobility issues”, it’s more like carelessness.

Remember as well that you don’t need to be perfect, nobody is acting or expecting that. All we can all do is try our best and if we hurt people, take accountability and apologise to them. No one always gets it right and it’s okay to get it wrong, so long as you’re not being stubborn and refusing to change because you don’t care about the feelings of others, people will be fine with it!