  We critically reexamine two possible Dark Matter candidate within the
Standard Model. First, we consider the $uuddss$ exa-quark. Its QCD binding
energy could be large enough to make it (quasi) stable. We show that the
cosmological Dark Matter abundance is reproduced thermally if its mass is 1.2
GeV. However, we also find that such mass is excluded by the stability of
Oxygen nuclei. Second, we consider the possibility that the instability in the
Higgs potential leads to the formation of primordial black holes while avoiding
vacuum decay during inflation. We show that the non-minimal Higgs coupling to
gravity must be as small as allowed by quantum corrections, $|\xi_H| < 0.01$.
Even so, one must assume that the Universe survived in $e^{120}$ independent
regions to fluctuations that lead to vacuum decay with probability 1/2 each.
