Step to the side, but, plant a stinky fart for them to walk into.
I do this all the time on the subway. Some kid is just acting like raging lunatic, while his/her parent is telling them to calm down. I then push a putrid fart (crop dust or drop and scramble) and watch the kid lose their shit even more; "
Eeeeeeewwww!! Somebody farted!! Aaaaaaghhh!! It smells so bad!!!" And then the parent tries even harder to get them to be quiet.
I also fart when people walk right up to me and pretty much press themselves against me, which is surprisingly common, on a train that isn't even really crowded!
Or bump into me, without saying
excuse me - I follow them to expel my ordinance.
If you enter my personal space because it's crowded or by accident, it's all good, no worries.
However, if you are a thoughtless goon (man, woman or child) who enters my personal space, the gas will be released.