If a guy is shoving every single hand...

[Kurn]

OK. In a SNG, HU assuming high blinds, theoretically the ONLY way to deny an opponent shoving any 2 cards +CEV is to call with any 2 cards. If you fold at all, those folds give him positive equity.

That's in the long run. Reasonably, waiting until you get a hand that has +equity over a random hand makes the most sense since you aren't going to play a million SNGs HU against this guy.

In a cash game, it is much different, and you'd better be sure he's going to stick around if you call and lose. let him keep shoving and keep taking your blind. Just keep reloading and you'll eventually get him.

This is where live games are better than online. In online NL games you can only buy-in to the designated table maximum. In most casinos, while there is a stated max buy-in, you can usually buy in up to the however much the biggest stack at the table has.