Stam yainam is d’rabanan, modeled on yayin nesech model. Is there a hanaa issue also? Can I re-gift it to a non Jew?
The status of stam yeinam for purposes of deriving benefit depends on who produced it.
If the wine is manufactured by non-idolaters, it is permitted to derive benefit from the wine by giving it to a non-Jew.
Because it is hard to know who manufactured the wine, and because of the general decline in religious belief (this can depend on where the wine was made), there is room for leniency. If it was manufactured by Christians, there is a dispute among authorities as to whether it is permitted or not, and there remains room for leniency, certainly where some loss is involved (for instance, where an alternative gift will have to be bought to replace the wine).
This answer does not address the general question of giving gifts to non-Jews, which we have addressed elsewhere.
See Tur, Shulchan Aruch, and Rema, Yoreh De’ah 123:1, where two opinions are cited concerning today’s idolaters; Shulchan Aruch 124:6 (concerning a non-Jew who we know does not worship idolatry); Taz 123:2 (permits where there is a loss); see also Shoel Venishal 6:142; Ben Ish Chai Balak 4; Yashiv Moshe 1:203.
Although the prohibition of setam yeinam does not apply to wine that has been cooked (boiled or heated to a high temperature; see Minchas Yitzchak vol. 7, no. 61), in the case of non-kosher wine, the concern is that the wine was handled and poured by non-Jews before the heating process (for pasteurized wine), and the stringency would therefore remain.