If one eats at a restaurant, but eats outside where there are tables and chairs, does that invalidates one from testimony? Are there any poskim that address eating outside at a restaurant?
Rashi explains that the reason why one who eats outside is invalid to give testimony is because he does not care about basic dignity. This is clearly not relevant to those who eat in a place where it is quite normal to eat.
I found in Sefer Devarcha Yair 2:34 who discusses this issue in depth bringing all sources. If you want to see all the back and forth see the teshuvah inside.
His conclusion :
- It is not proper for a Talmid Chacham or Ben Torah to eat in public even if its an area with a small amount of people. So too they shouldn't drink even water in public.
- For a regular person it is prohibited to eat in a major public area(main street) even if it isn't a gluttonous type of food. Nevertheless , if one did eat in such a place they do not lose their status of being a kosher witness since nowadays people do not view such eating as prohibited or degrading.
- In a place where it is common to eat in public such as a bus, or restaurant it is permitted even for a Talmid Chacham to eat in public.
Rav Meir Mazuz in hi Mekor Neaman was asked if one eats a set meal in a park is it considered like the prohibition of eating in public? He answered that if one sits on a bench and eats in a respectable fashion then its permmisble.
Text of Devarcha Yair 2:34 :
Text of Mekor Neaman 1:275 :