The Gemara in kiddushin mentions that eating in public is a disgraceful behavior and would invalidate a witnesses testimony. Does this still apply today? Why is this act considered so bad in the eyes of chazal. In current times, I believe most people wouldn’t think so bad of a person who eats in public.
This is an interesting question. Note that the halachah is ruled in the Shulchan Aruch (34) without objection.
It is certainly not disgraceful behavior to eat in a restaurant. Although this is “eating in public,” the public area of a restaurant is considered respectable, and will certainly not affect one’s status as a witness.
However, there are acts of eating in public that remain dishonorable (such as eating a pizza on a bus), and these are the ones to avoid. Indeed, the wording of the Gemara is that one who “eats in the market” is invalidated, and this implies a specific mode of eating in public that Chazal denigrated.
Note that the halachah of being invalidated for testimony applies specifically to an actual “se’udah” in public, and not eating a chocolate.
Even for eating in a way considered disrespectful, there remains room to consider how the principle will be applied today – it is possible that the degree of contempt in which somebody eats in public has changed, and this might influence the halachah.
In my own experience I have never seen somebody invalidated for testimony for this reason, and it is a little hard to conceive of this happening.