If you don't make it clear people will think you're serious.

Sarcasm doesn't work online, If I write something like "Donald Trump is the best president ever" you don't have any way of knowing whether I'm being sarcastic or I'm just really really stupid. Only people who know me can make that judgement, and basically nobody on here knows me. So I either have to avoid sarcasm or make it clear that I'm being sarcastic.

Context of the comment would tell