It would more likely fall under naizuri than paizuri, assuming it even falls under either of these two options.
Anyways, here is an example of the imagery you're referring to, post #1392426, which has a trap performing it on a man.
Posted under General
I guess that could qualify as a form a paizuri, though it should be pointed out that currently naizuri and paizuri are mutually exclusive. Depending on the approach taken for a tag to categorize males performing the act, a similar divide would likely exist with that tag as well for dividing those with "boobs" and those without.
Possible approaches:
Just a bias opinion based on what I've seen, but I'd think an image of a male performing any of these acts would be rather niche and very low population, and even more so for a male with "manboobs" doing it (not taking into consideration things like shemale/newhalf). I would not expect that we'd likely end up with images of males performing "paizuri" with their manboobs. Sure it may future-proof it to work out not running into a problem with them, but the likelihood we'd have it, particularly as approvable content, to me seems extremely low. So I do not think it's really going to be that major of a risk to worry about, regardless of our approach on this.
apologetic necrobump
I found out a while ago that the pixiv tag is "男パイズリ" (male paizuri). As for the possible tagging approach, I think that the third option might be the best of the four, since I highly doubt that users would want to run in men giving paizuri when searching for said tag.
The two tags could be "male_paizuri" and "male_naizuri," without implicating the original tags.