Glass cups-May one drink from wine glasses of a non-Kosher bar, hotel lobby, or restaurant:
It is permitted to drink from the clean glass cups of a gentile. This applies even if the cups were used in the past to drink Yayin Nesech and were washed in hot water with non-Kosher food. One may even use the glass to drink a hot beverage [so long as the beverage and hot water used does not contain any Kashrus worry]. This leniency applies only towards glass cups, and not to cups made of other materials!
 See Admur 451:73 for the various opinions regarding glass; M”A 451:48 and Poskim in Darkei Teshuvah Y.D. 121:2 that we are lenient by other Issurim; Admur 451:2 that in a time of need one may use a non-Kosher vessel for cold foods
 The reason: a) By other Issurim and Yayin Nesech we follow the opinions [Admur 451:73] who rule that glass does not absorb, and hence is never considered not Kosher. [M”A 451:48; Poskim in Darkei Teshuvah Y.D. 121:2; See article on “The status of glass” for the full details of this subject]; b) One may use a non-Kosher vessel for cold foods in a time of need. [See Michaber Y.D. 91:2 and Poskim there; Admur 451:2]
 See 1st reason above!