Question: Am I allowed to meet people in a coffee shop if they are eating non-Kosher food and I am just having a coffee?
Answer: The Mishna (Shekalim 3:2) writes that the person who took the teruma from the shekalim in the Beis Hamikdash had to ensure that they were not wearing shoes or that their clothes had any pockets, etc. so that no one could falsely accuse them of stealing any money. While this prohibition is typically referred to as maris ayin, R’ Moshe Feinstein (Igros Moshe OC 2:40; 4:82) explains that there are, in fact, two separate prohibitions.
Maris ayin means that one should avoid doing something which will easily lead people to jump to the wrong conclusion that something else is permissible. Therefore, one should avoid going to daven in a shul that lacks a mechitza even if one is going to daven in a separate room, as others may think that it is permissible to daven in such a shul.
Chashad, on the other hand, is giving others the impression that one is performing an averah. This prohibition is more severe, and according to R’ Moshe, is assur mideoraisa. Sefer Chinuch (295) stresses that this prohibition is even more severe for prominent people such as Rabbis.
One eating in a non-Kosher restaurant could potentially transgress both chashad and maris ayin, though one is allowed to enter under extenuating circumstances. One doing so should go in an inconspicuous manner and ensure that no one outside recognises them without knowing why they are entering.
Although coffee shops sell non-Kosher food, one may eat there as we are not concerned that people will assume that they are eating non- Kosher food, nor that the non-Kosher food there is Kosher (See Igros Moshe OC 1:96).
In conclusion, one may have a coffee in a coffee shop that also sells non-Kosher food.