The only real context through which it is appropriate to use the phrase "mostest" is immediately after the words "I like you the". "Bestest" can be appropriate On this context (and no other). Stack Exchange network consists of 183 Q&A communities like Stack Overflow, the most important, most trusted https://financefeeds.com/bpx-secures-fca-approval-to-operate-regulated-marketplace-for-traditional-and-tokenised-securities/