In case the other explanation isn't plain enough:

• Smoking is a controversial habit
• People who don't smoke often (rightfully!) highly object to being exposed to it, and sometimes they do this in exaggerated or dramatic ways
• People who do smoke are sometimes offended by other people's disgust or demands to not be exposed to smoke, and this can sometimes develop into disdain for what they perceive as weakness

The joke, as I understand it, is that it is extremely silly to believe a toddler is doing exaggerated, dramatic response to smoke exposure, and it is silly for a smoker to be offended by the response of a small child, especially so offended that they're posting about it.

I should probably note that I'm also neurodivergent and sometimes wildly misunderstand humor and find things funny for entirely different reasons than neurotypical people do, so this could all be wrong. This is why I found it funny.

Also, I usually smoke a few cigarettes when I drink, and if I'm currently involved in outdoor conversation, I do stuff like hold my cigarette hand straight up above me and constantly watch the wind direction to keep smoke away from other people as much possible, whether they smoke or not. If I'm not actively chatting, I will go walk around by myself or find a spot away from everyone's airspace to check my phone. I don't find it particularly difficult to be respectful and considerate of other people's right to breathe clean air.