I tweet a good bit during the day, and almost always without fail my boyfriend is the first to throw a like on my posts, sometimes to a point that the like notification seems to come in the second I actually post my message.
He's fast, and after the first month or so of his quick-draw likes I remember asking him if he was using a bot to just blindly like my posts. Turns out, he had actually set up a notification so he gets a pop-up on his desktop when I tweet something new. He takes my tweets as an opportunity to take a short break, and clicks through the notification to see what I wrote and in most cases like it.
While he isn't using a bot, I discovered this week there's actually one out there for Instagram.
With it, you set things up to auto-like a particular user's posts. When the like is sent, you'll get a message in Slack letting you know it happened so you can actually check out the post yourself. And you should absolutely look at that post ASAP rather than make someone think you saw (and liked) something you didn't. The idea here is to avoid a "Why didn't you like X" conversation when you're super busy, not entirely remove yourself from the equation.
The bot is available as a free download on Github. Its creator, gulzar 1996, created it as a way to auto-like his girlfriend's posts. For now, it only works for Instagram, but he has plans to add Twitter support as well as a layer of facial recognition in the future, so you could potentially only like pictures that include your friend (or significant other's) face instead of everything in their timeline.
Another good option: just setting up notifications for when your friend posts. You can do that by going to his or her profile on Instagram and tapping the three dots on the top right side of the page. From there, select "Turn on Post Notifications" to get a push notification from the Instagram app each time a new post comes in. Then you can like it for real.