‘Apeing’ refers to participating in a crypto project without performing due diligence or DYOR. This term became popular during the summer of 2020 (‘DeFi Summer’), when new and unannounced tokens were being launched at an extremely fast pace and many individuals felt they didn’t have time to do their own research and would just buy without establishing firsthand knowledge.
On a slang slant, it is derived from the phrase ‘go ape’, as in going wild. Individuals ‘ape’ into new tokens usually because they have a fear of missing out (FOMO), which is a feeling that they will potentially miss a great opportunity unless they buy early enough.