By exploiting photometry from the Wide-field Infrared Survey Explorer (WISE), we investigate the influence of environment and stellar mass on the prevalence of different excitation types in the interstellar gas of central regions of galaxies in the Herschel Reference Survey (HRS, z~=0.0047). This analysis is extended to a complementary sample of relatively nearby galaxies currently undergoing ram-pressure stripping (RPS, z~=0.0195). Our goal is to assess whether a connection exists between active galactic nucleus (AGN) activity and either the cluster environment or the ram-pressure stripping process. We compute WISE mid-infrared colour indices from fluxes extracted from central apertures and apply two established mid-infrared diagnostic diagrams to distinguish AGN activity from non-AGN, and star-forming galaxy (SFG) excitation from that associated with "retired" galaxies. The resulting types of excitation are then used in conjunction with stellar mass and environment classifications to construct a stellar mass-excitation fraction relation. The stellar mass-excitation fraction relation reveals that global stellar mass is the primary driver of excitation diversity in galaxy centres. In increasing order of prevalence, excitation types follow a sequence from SFG to retired galaxies with increasing mass. The number of low-mass galaxies is too small to drive statistical tendencies. In contrast, SFG excitation becomes dominant at intermediate masses. At the highest mass end, retired-galaxy clearly prevails. SFG is the most common across the full mass range and in nearly all environments, except for HI-gas deficient HRS galaxies, which are mostly retired. The excitation properties of galaxies undergoing RPS resemble those of HRS cluster members, field, and normal HI-content galaxies, minimizing the environmental role. Contrary to previous results, we do not see any increase of the AGN activity in HI-deficient cluster galaxies nor in those undergoing RPS since its fractions (~10% for Sy2 and ~20% for LINER) remain largely unaffected along all environments. These findings indicate that while rich environments are associated to certain excitation types, stellar mass remains the primary driver of excitation diversity in galaxy centres.