>>12350840On a surface level, the joke is just that it's a bad pickup line based on real world statistics that whites will soon be a minority as a result of declining birth rates.
On a deeper level, it's a comic from the LA Times and written by a leftist, so he's actually trying to make fun of the (mostly right wing) people who "care" about white replacement. "Comics" like this are so low T and consumed by ideology that they see their own replacement as a good thing that should not be questioned, talked about, or impeded